Technical Field The present invention relates to a loading ledge, comprising an L-shaped profile having projections for supporting a load at a certain distance over a support. Background of the Invention The conventional1 way to distribute palletized articles is by using traditional pallets, most often wooden pallets of standardized dimensions, on which the articles are loaded. Attempts have been made to mould such pallets in plastic, an example being given by US-A-3 702 100. The supporting feet of these particular, mostly traditional pallets are provided with internal ribs. In view of the numerous disadvantages with such traditional pallets, attempts have been made to replace such pallets by other loading members. A relatively recent example is the loading ledge shown in WO-A-02/38471. The load bearing capacity of such a loading ledge is generally governed by that of the projections. Measures have already been taken to improve the strength of the projections. However, it has been felt that further improvements with regard to load bearing capacity of the projections and thus of the loading ledge as a whole would be highly desirable. The Invention Such improvements may according to the invention be attained by the combination of generally vertical reinforcing corrugations in the sidewalls of the projections and internal reinforcement ribs in the bottoms of the projections, said ribs extending to the sidewalls of the projections. Calculations and practical tests of a certain embodiment have shown that before actually collapsing under an excessive load, the sidewalls of a projection will bulge out, mainly at their lower portion close to the bottom of the projection, whereas the bottom of the projection will have a tendency to bulge up or inwardly. In another embodiment the sidewalls will instead bulge in before collapsing. These tendencies are prevented by the reinforcement ribs, so that a higher load can be handled by the projection without adding to the material thickness or improving the material quality. The load bearing capacity may be increased in the order of 20 % or even more. The reinforcement ribs may extend in the longitudinal direction of the loading ledge or perpendicularly thereto. Another possibility is that the reinforcement ribs extend both in the longitudinal direction of the loading ledge and perpendicularly thereto in a grid pattern. In a projection with a considerably greater length than width it may be most effektive only to have ribs in the perpendicular direction, whereas the grid configuration may be preferred in a projection with substantially square bottom. In a practical case each reinforcement rib can have a height of 8 mm and a width of 3 mm. Brief Description of the Drawings The invention will be described in further detail below under reference to the accompanying drawings, in which Fig 1 is a perspective view from above of a loading ledge, Fig 2 is aperspective view from below of the loading ledge shown in Fig 1, Fig 3 shows the loading ledge of Fig 2 in a substantially fully loaded condition, Figs 4-6 are plan views of a lateral projection of the loading ledge incorporating an arrangement forming part of the invention, and Fig 7 is a perspective view from above of a central projection of the loading ledge incorporating an arrangement according to the invention. Detailed Description of Preferred Embodiments A loading ledge 1 is shown in Fig 1. It is a preferably injection moulded, L-shaped profile of recyclable plastic, preferably polypropylene (PP) . Its lower leg 2 is provided with projections or feet 3, in the shown case three projections, for supporting a unit load above the ground or other support and allowing handling with ordinary handling equipment utilized for goods on ordinary wooden pallets presently widely used in distribution systems. Its upper leg 4 is generally plain and is to bear against a vertical side surface of a unit load to be supported by the loading ledge. In a practical (but non-limiting) case the overall length of the loading ledge 1 may be 760 mm and the widths of the lower leg 2 and the upper leg 4 180 mm and 100 mm, respectively. The projections 3 may have a height of 35 mm and a width of 75 mm. The central projection may have a length of 160 mm, and each of the two outer or lateral projections may have a length of 75 mm. A unit load (for example consisting of several packages) is to be placed on two or more loading ledges 1 and preferably provided with straps and/or stretch or shrink wrapping. For a reasonably large unit load two loading ledges 1, placed opposite each other at lower edges of the unit load, may be sufficient, but for larger unit loads two or even more loading ledges may be arranged at each lower edge. It is also possible to use four loading ledges 1 on a unit load, one at each lower edge, for example if the width of the unit load is considerable. Each loading ledge 1 may be exposed to a considerable weight or load, and the most critical portions for assessing the maximum permitted load for a loading ledge is its projections 3. Among the parameters for determining the maximum load on the projections 3 (and thus on the loading ledge 1) are the material choosen, the material thickness, the height of the projections, and the inclination of the sidewalls of the projections. One important meaure to improve the load bearing capability of the projections 3 is to provide their sidewalls with corrugations as illustrated in Fig 7. For the sake of clarity, however, these corrugations are omitted in the other Figures. > Both practical tests and calculations of a certain embodiment have shown that prior to finally collapsing the projections 3 will assume the shape illustrated in Fig 3, i e the sidewalls of the projections will bulge out rather close to their lower ends, whereas there will be a tendency for the bottom of the projections to bulge in or up. (In another embodiment the sidewalls will bulge in.) A considerable improvement in this respect may according to the invention be attained in that the bottoms of the projections 3 are internally provided with reinforcement ribs 5 extending to the sidewalls of the projections, in combination with the sidewall corrugations. Three illustrations of possibilities to practically arrange such reinforcement ribs 5 are shown in Figs 4-6. Each of these Figures shows a lateral or end projection 3 of a loading ledge from above. For the sake of simplicity the projection is shown with plain sidewalls, i e without the reinforcing corrugations that are provided in a practical case. The bottom of the projection is provided with a drainage hole 6. In Fig 4 four reinforcement ribs 5 extend perpendicularly to the longitudinal direction of the loading ledge 1. In Fig 5 two reinforcement ribs 5 extend in the longitudinal direction of the loading ledge 1. In Fig 6 four reinforcement ribs 5 are provided in both directions in a grid-like pattern. Fig 7 is a perspective view of an actual central projection with reinforcing sidewall corrugations. The bottom may be provided with say eight reinforcement ribs 5 perpendicularly to the longitudinal directions of the loading ledge 1, as is also illustrated in Fig 4. The lateral or end projections of the same loading ledge as is illustrated in Fig 7 may have the reinforcement rib arrangement shown in Fig 6. Practically, the ribs 5 may have a height of 8 mm and a width of 3 mm, but other dimensions are possible. The ribs 5 may be of slightly conical shape in order to allow tool clearance. The improvement in load bearing capacity of a projection provided with sidewall corrugations, also provided by the reinforcement ribs 5 may be quite considerable, or in the order of 20 %. If the load bearing capability for a loading ledge without reinforcement bottom ribs 5 is in the order of 1000 kg, it may increase to about 1200 kg with reinforcement ribs 5, which is of great importance in many applications. The reinforcement ribs 5 provide the extra advantage that loading ledges 1 stacked on each other do not stick together in the projections 3 as they do without bottom ribs 5. In principle, the advantages with the reinforcement ribs 5 increase with increased height of the projections 3. In order to allow more space between the projections 3 for load handling equipment, sxich increased height is a practical possibility.