EMI: Change drawing order of faces

If multiple faces of one model are referring to the same triangles, let
them overwrite each other so that the latest one will be visible. For
this purpose glDepthFunc is changed from GL_LESS to GL_LEQUAL so
that subsequent drawing attempts for the same triangle are not ignored by
the depth test.

This fixes the issue of the colored leg of the monkey bot in the end
scenes: the leg is drawn using color maps by the first face and using
textures by a following face.