Restore MD3 code for cg_shadows 2 and 3 like other model formats.
Fix planar projection shadow deform (cg_shadows 3) to use correct
light direction. I fixed light direction for stencil shadows
(cg_shadows 2) but it's still broken.
Stencil shadow is not drawn if a mesh, or multiple meshes with the same
entity and shader, have more than 500 vertexes. The issue is caused by storing
the projected positions in the tess vertex buffer. Use a new array instead.
