ONE PIECE GUTTER WITH INTEGRATED SCREEN FIELD OF THE INVENTION The present invention relates to eavestrough or rain gutter, and more particularly, relates to improvement in such structures. BACKGROUND OF THE INVENTION Various types of gutters or eavestroughs are well known in the art as is the use of shields or cover members therewith. The purpose of the shield is essentially to permit passage of rainwater from the roof to the eavestrough while protecting the same from extraneous foreign matter such as leaves and the like. There have been many different approaches taken to the design of eavestroughs which incorporate such shields. Indeed, a commercially available eavestrough utilizes a cover which has an outer edge which curls downwardly and the water flow follows the curved portion due to surface tension and thereafter cascades into the eavestrough. Leaves and other extraneous matter are supposed to fall exteriorly of the eavestrough. However, when a large volume of water flows, the surface tension is generally insufficient to cause all the water to flow into the eavestrough. The art is also replete with examples of various shields or guards which are apertured and permit the passage of rainwater while supposedly barring the passage of extraneous material. However, many of these guards do not function as desired and access must often be had to the eavestrough for cleaning purposes. A further problem associated with such shields or guards is the connection of the same to the eavestrough. To this end, many complex arrangements have been proposed in the art. In order to overcome the above disadvantages, there have also been proposals in the art for one piece eavestrough which are secured to clips which are fastened under roof shingles. One integrated eavestrough with a cover member is shown in U.S. Patent 4,727,689 to Bosler. However, in many situations, the design of the roof and fascia is such that one could not attach the clips and subsequently fit the eavestrough therein. In other words, one requires a certain amount of space between any overhang and th clip. In many situations, the gutter must be secured proximate to the roof overhang at one end of the eavestrough and this would be very difficult to achieve with the prior art structure. A further problem with such clip and eavestrough arrangements is the snow loads which occur in Northern climates. Thus, the snow load could cause the gutter to fall from its mounting arrangement with the clip. SUMMARY OF THE INVENTION It is an object of the present invention to provide an integrated eavestrough and shield or guard therefor, and which integrated eavestrough overcomes the disadvantages of the prior art. According to one aspect of the present invention, there is provided an eavestrough formed from a single piece of material, the eavestrough comprising a rear wall, a front wall, and a bottom wall, said rear, front and bottom walls defining a trough therebetween, a top wall extending between the front wall and the rear wall to cover the trough, the top wall comprising, a first top wall section extending inwardly form an upper end of the front wall, a second top wall section extending downwardly from the first top wall section, a third top wall section extending across the trough, the third top wall section having a plurality of apertures therein to permit water drainage therethrough, a fourth top wall section extending upwardly alongside an upper portion of the gutter rear wall, a locking section extending downwardly from the fourth top wall section rearwardly of the rear wall and engaging the rear wall in a locking relationship. In a further aspect of the present invention, in a building having an eavestrough for draining rainwater from a roof and wherein the eavestrough is attached to a fascia of the building, there is provided the improvement wherein the eavestrough is formed from a single piece of material secured to the fascia, the eavestrough comprising a rear wall, a font wall, and a bottom wall, the rear, front and bottom walls defining a trough therebetween, a top wall extending between the front wall and the rear wall to cover the trough, the top wall comprising, a first top wall section extending inwardly from an upper end of the front wall, a second top wall section extending downwardly from the first top wall section, a third top wall section extending across the trough, the third top wall section having a plurality of apertures therein to permit water drainage therethrough, a fourth top wall section extending upwardly along side and upper portion of gutter rear wall, a locking section extending downwardly from the fourth top wall section rearwardly of the and engaging the rear wall in a locking relationship. The one piece eavestrough of the present invention may be formed from any suitable material with a preferred material being aluminum. The eavestrough may be manufactured using a roll forming technique. As previously mentioned, the device of the present invention prevents foreign matter from entering into the eavestrough. In order to do so, there are provided a plurality of apertures to permit the passage of rainwater and to prevent extraneous matter from entering the gutter or eavestrough. In general, it is desirable that the apertures be sized large enough to permit the passage of rainwater while preventing the entry of extraneous matter into the trough. Generally, apertures in the range of between 3 and 4 mm may be utilized. BRIEF DESCRIPTION OF THE DRAWINGS Having thus generally described the invention, reference will be made to the accompanying drawings illustrating an embodiment thereof, in which: Figure 1 is a perspective view of a portion of an eavestrough according to the present invention attached to a structure; Figure 2 is a cross sectional view of an eavestrough in an assembled condition according to the present invention; and Figure 3 is a perspective view of a portion of an unassembled eavestrough of the present invention. Referring to the drawings in greater detail and by reference characters thereto, the eavestrough of the present invention is designated generally by reference numeral 10. Eavestrough 10 includes a bottom wall 12 which has a plurality of longitudinally extending ribs 14 formed therein. Extending upwardly from bottom wall 12 at one edge thereof is a rear wall generally designated by reference numeral 16. Rear wall 16 includes a lower vertical portion 18 and an inwardly extending recess 20 formed proximate the upper end of rear wall 16. At its upper end, recess 20 is defined by an outwardly extending wall portion 22 which continues on to terminate in a vertical portion 24. A front wall of the eavestrough 10 is generally designated by reference numeral 26 and includes a lower vertical section 28 and a main arcuate section 30. Arcuate section 30 terminates in a top vertical section 32 which merges with a top wall 34 and a downwardly extending vertical wall section 36. Sections 32, 34 and 36 together define an inverted generally U-shaped configuration. In this regard, it will be noted that top wall 34 slopes downwardly from its outer edge where it merges with top vertical section 32 to the point where it merges with downwardly extending vertical section 36. Preferably, the slope is between 2 and 10° and more preferably, between 4 and 6° from the horizontal. A top wall 38 extends inwardly and includes a plurality of apertures 40 to permit drainage of rainwater therethrough. At the opposite side of top wall 38, there is provided a rear vertical section 42 which merges with a rearwardly angled section 44. At its distal end, rearwardly angled section 44 merges with a downwardly extending vertical section 46 which terminates in an inwardly extending hook portion 48. Inwardly extending hook portion 48 is designed to engage outwardly extending wall portion 22 of recess 20 such that the structure forms an integrated one piece eavestrough. It will be noted that top wall 38 slopes slightly downwardly from wall section 36 to rear vertical section 42. Preferably, the slope ranges between 3/16" an 3/8". In operation wall sections 36 and 42 are designed to act as barriers to retain the water on th eavestrough during any heavy rain fall to thereby permit time for the rainwater to pass through apertures 40. Preferably wall section 36 will have a height of at least 75 mm with wall section 42 having a height of at least 150 mm. The eavestrough is secured to the building B through vertical section 42 by suitable attachment members such as screws 60 or the like. This permits the eavestrough 10 to withstand snow loads in Northern climates. Furthermore, the use of screws with automated equipment makes installation of the gutter a relatively simple operation.