CENTRIFUGAL SCREEN APPARATUS This invention relates to centrifugal screen apparatus This invention has particular but not exclusive application to centrifugal wire screen apparatus for mineral processing, and for illustrative purposes reference will be made to such application. However, it is to be understood that this invention could be used in other applications, such as perforated centrifugal screens generally. PRIOR ART Centrifugal screens are widely used in the mineral processing art. In particular centrifugal screening forms a usual part of processing coal slurries, capable of continuously wet screening high volumes of material. In general a coarse-coal centrifugal screening apparatus is as illustrated in representative prior art Fig. 1. Fine coal centrifugal screening apparatus may further include screen scrapers and may be vertically mounted. The screening element may be presented as a bolt-up screen member supported on a screen support. The principal wear component is a rotating, commonly frusto-conical wedge wire basket. The basket has a wedge wire screening surface where the wires run in axial planes to provide for product shear in use. The basket is formed from wedge wire screen stock. To account for the fact that the wedge wires are parallel while the conical form is divergent, the screening surface is defined an assembly of trapezoidal sections cut from flat wedge wire screen stock and pressed to form a segment of a conical surface. Wedge wire screen stock generally comprises wedge wires interconnected by spaced cross bars welded to the back of the wires at the intersections. Alternatively the stock may be produced with no cross bars but a continuous MIG weld or back-weld in lieu of the cross bars. The cut sections have the wedge wires running between the prospective ends of the conical structure with the cross bars or back welds in transverse orientation. The sections are then welded together at the points of contact at the back, generally at the butt join of the cross members or back welds and contact lines between corresponding tapered cuts on the wedge wires. A drive end terminal flange is generally welded to the narrow end of the conical form of the wedge wire screening surface, and a discharge end terminal flange is provided at the other end. In order to stiffen the structure against torque loading in use, there are generally provided welded-in stringers which stretch between the end flanges, and intersect steel hoops which conjointly define a support for the screening surface. In the case of fine coal centrifuge baskets, a wedge wire screening member is provided with means allowing the bolt up of the screening member to a separable screen carrier. A drive plate is generally secured to the drive end flange within the housing whereby the basket may be rotated. The open end of the basket provides an inlet to admit material to be screened to the inside of the basket. The housing has an open face opposite the drive flange end to allow installation of the basket, the open face being selectively closed by a door that generally includes an inlet conduit adapted to extend into the basket to deposit material to be screened at the narrow end. The housing may have one or more drain outlets to allow egress of material passing through the screening surface from the housing. The housing at the open end of the basket may be provided with an outlet for material retained on the screen and migrating along the taper of the screening surface. Maintenance involves replacement or refurbishment of the basket. The basket is a heavy item. In particular, the supporting frame is heavy to account for the significant centrifugal and driving loads, exacerbated by the anisotropy of the material feed. Large baskets may weigh in excess of 300 kg. Maintenance accordingly requires the use of lifting gear. Customer research has indicated a need for a safer and more user friendly centrifuge basket change over during shut-downs. DESCRIPTION OF INVENTION This invention in one aspect resides broadly in a centrifugal screen adapted to be mounted for driven rotation within a housing and including an annular screen support and a screen surface member resiliently mounted within said annular screen support. By providing a resiliently mounted screen element, the weight of the principal wear component of a coarse coal centrifuge is greatly reduced. By resiliently mounting a fine coal centrifuge basket, specific advantages may accrue as described hereinafter. Prior art coarse coal and other centrifugal screens are generally formed of steel. The annular screen support of the present invention may be formed of an abrasion resistant material whereby said screen support is replaceable on a longer cycle than the screen surface member. For example, the screen support may be formed of stainless steel or a composite material or may comprise a substrate covered with a wear resistant polymer such as polyurethane. The screen support may take any suitable form consistent with being able to be mounted in driven rotation within the housing and permitting the material passing through the screen surface member to pass through to an outlet provided in the housing. Typically the screen support will comprise a drive end including means for driving the screen support and a free end. For example, the screen support may comprise at least a drive end plate and a free end annulus. The free end open annulus may be defined by a flange which in use runs proximal a closure plate or door for the housing, the plate or door being provided with a central aperture through which a conduit may deliver the material to be screened. The drive end plate may be integral or may comprise an annular flange closed by a plate. The drive end plate may be adapted to form a removable intermediate-wear component that may be replaced on a longer cycle than the screen surface member. The drive end plate may be adapted to accept the rotational driving force by any suitable means. For example the drive end plate may be adapted to be bolted through to the drive flange of a motor and gearbox assembly mounted coaxially through the end of the housing. The screen surface member may presents a surface of a shape selected from substantially cylindrical, substantially polygonal, and substantially frusto- conical, and is rotatable assembly rotatable about its major axis. In the case of centrifugal screens of constant cross section along the axis of rotation, the screen element may comprise a plurality of screen panels. For example, a polygonal screen may comprise a plurality of flat wedge wire panes adapted to be releasably secured to the screen support. A cylindrical screen may comprise a plurality of part-cylindrical panels. The panels may be adapted to be secured by their longitudinal edges to complementary engagement means provided on the stringers of the screen support. For example the panel edges may comprise a rigid or resilient profile adapted to be removably engaged with a complementary resilient or rigid profile provided on the stringers. As such the complementary engagement means may comprise a resilient clip-in section of the type including a longitudinal recess having a narrow opening and adapted to receive a longitudinal element on the other part, longitudinal element being adapted to deform the opening of the recess under engagement forces to be clipped into the recess and retained thereby. The panel edges may be configured to resist the ingress of fines into the panel joins, and by doing so avoid or reduce abrasive wear of the profiles. For example, there may be a resilient insert entrapped between the respective panel edges, or the panel edges may be configured to cooperate to form an effective labyrinth. The drive end plate and/or outer flange of the screen may be further adapted to locate the end edges of the panels. The number of panels may be selected according to the number of longitudinal stringers which are available to provide the complementary mounting of the panels to the screen support. The number of panels may also be determined having regard to the weight of the individual panels, with it being preferred to limit the individual panel weight to at most 20kg and possibly down to a one-man safety limit of 16kg. Frusto-conical screen apparatus presents particular technical issues and possibilities. The invention is described hereinafter with reference to frusto- conical screen assemblies, although many of the principles described hereinafter are relevant to the construction of other centrifugal screen assemblies. In essence, all of the advantages of the aforementioned embodiments accrue to a frusto-conical screen in accordance with the present invention. In addition, the usual configuration of the screen entering the housing narrow end first may be utilized to advantage in apparatus in accordance with the present invention. For example where the frusto-conical screen includes a unitary screen surface member, the means for providing engagement between the screen surface member and the screen support may comprise complementary engagement means adapted to cooperate to be fully engaged by axial advancement of the screen surface member into engagement with the screen support member. As such the complementary engagement means may again comprise a resilient clip-in section of the type including a longitudinal recess having a narrow opening and adapted to receive a longitudinal element on the other part, longitudinal element being adapted to deform the opening of the recess under engagement forces to be clipped into the recess and retained thereby. In this case the engagement force may be provided by axial advancement of the screen member into the screen support until the engagement is effected, whereupon the screen member may be retained against a disengaging end float by any suitable means. In frusto-conical embodiments comprising a screen member comprising a plurality of screen panels, the panels may be again adapted to be secured by their longitudinal edges to complementary engagement means provided on the stringers of the screen support. In one embodiment of the present invention the panels are provided with a round bar or other suitable profile bars welded to the back of wedge wire stock along the prospective trapezoidal long edges of the panels, which are then cut and pressed to curvature. The stringers may be adapted to mount or receive a resilient body having the recess, preferably in adjacent pairs to accept the profile bars of adjacent panels in the assembly. In the alternative there may be provided a single recess, whereupon the profile bars may comprise complementary pairs whereby the panels may be installed with the complements in abutment. The resilient body may be substantially continuous along the stringer or may be located at discrete locations. The end portions of the screen may be further adapted to locate the end edges of the panels. Particularly in the case of a frusto-conical screen member comprised of panels the outer end flange may be adapted to simply block the panels from disengagement by blocking end float. In the alternative or in addition thereto the retention of the screen member may be by locking means operable between the screen member and the screen support. For example, there may be provided means associated with the stringers and adapted to engage the outer rim portion of the screen member such as at the terminal cross member, this limited retention being made possible by the taper of the conical arrangement limiting the movement to outward end float. The mounting of the resilient body may be by means of a metal profile formed on the stringer and adapted to receive a resilient insert. The metal profile may be welded to the stringer. In particular embodiments of the present invention the mounting of the resilient body comprises a generally U-shaped section which is adapted to receive and retain the insert, the insert and U- shaped section in assembly being transversely bolted to the stringer. This constructions is particularly useful where each of the panel edges are provided with their own clip in profile, whereupon the insert and U-shaped section in assembly are bolted in pairs to each flat of the stringer. In a further aspect this invention in one aspect resides broadly in screening apparatus including: a housing; a screen assembly mounted for driven rotation within said housing, the screen assembly having a screen support member and a frusto-conical screen surface comprising a plurality of part conical screen panels each having a mounting profile adapted to engage in clip in relation a complementary resilient mounting profile provided on said screen support member. The screen support member and the clip in relationship may be as described above. The panels may comprise a part conical segment of the frusto-conical surface extending from the drive end to the open end of the screen support as described above. However, it is envisaged that the screen panels may include panels for particular axial extent so that the panels are axially arrayed as well as circumferentially arrayed. In these embodiments, the circumferential edges of the panels may be adapted to interengage with the circumferential edge of the axially adjacent panel. By this means the panel weight may be reduced in very large assemblies, with the penalty of having different panels for each circumferential array. BRIEF DESCRIPTION OF THE DRAWINGS In order that this invention may be more readily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention and wherein: FIG. 1 is an exploded view of prior art screen apparatus to provide context; FIG. 2 is an exploded perspective view of screen apparatus in accordance with the present invention; and FIG. 3 is a detail view in section of the mounting between the screen panels and screen support of the apparatus of FIG. 1. DESCRIPTION OF THE EMBODIMENT In the comparative Fig 1 there is provided a general arrangement of a screening plant and including a mounting chassis 10 having pedestals 11 adapted to receive a screen housing 12 on isolation mounts 13. The chassis 10 also mounts an electric drive motor 14 driving a transmission assembly 15, which drives a shaft and bearing assembly 16 mounted on the chassis 10. The shaft and bearing assembly 16 has an output flange 17 which is coaxial with the housing 12 and extends in sealed relation to the housing 12 through aperture 20. The housing 12 has an outlet chute 21 in register with an outlet space 22 through the chassis 10. The housing 12 is closed by hatch 23 that mounts an inlet conduit 24. A frusto-conical wedge wire screen surface 25 is supported on stringers 26 and hoops 27 to form a screen basket. A drive plate 30 is bolted to an inner terminal flange 31 of the screen basket, the drive plate 30 having an inner bolting flange 32 adapted to be bolted up to the output flange 17. In the embodiment of the present invention as illustrated in Figs. 2 and 3, the screen basket is replaced by a screen assembly made up of a stainless steel screen support 40 comprising annular flat bar hoops 41 interconnected by welding to stringers 42. At the inner end of the stringers 42 is welded an inner terminal flange 31 as per the prior art screen basket, and adapted to be bolted to the drive plate 30 and thence secured to the output flange 17. A wear plate 38 is welded adjacent the inner terminal flange 31. The outer ends of the stringers 42 are interconnected by an outer hoop 43 and circumferential stiffener 44. Six screen panels 45 are formed of wedge wire stock by cutting and pressing to curvature, and are provided on the back with welded longitudinal edge profiles 46 of round bar. The wedge wire stock is conventional and comprises wedge wires 47 interconnected with welded cross members 50. Mounted to each side of the stringers 42 between each adjacent pairs of hoops 41 are panel mountings comprising metal sections 51 within which are located resilient inserts 52 having a recess 53 formed therein. The inserts 52 are secured in the sections 51 , and the pairs of assemblies thereof are secured to respective flats of the stringers 42 by means of through bolts 54 and nuts 55. The ends of the cross members are relieved at 56. In use, a resilient joint seal 57 is laid on the edge of the stringer 42 and the edge profile 46 of a panel 45 is offered up to the appropriate recess 53. The profile 46 is driven into clipping engagement with the recess 53 by use of a mallet or the like, entrapping the resilient joint seal 57 at the reliefs 56 and between the wedge wire surface edges. The remaining panels 45 are likewise installed to form the wedge wire surface. The panels 45 are secured against end float disengagement by a retaining ring 60 adapted to be retained by metal threads to the outer hoop 43, which engages the outer edges 61 of the panels 45. To replace the panels 45 there is the simple expedient of opening the door 23 and removing the retaining ring 60, whereby the panels 45 may be pried out of engagement with the panel mountings, and the panels 45 and resilient joint seals 57 replaced. It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications and variations thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as defined in the claims appended hereto.