OpenGL2: Stencil shadow volumes are broken (cg_shadows 2)

[zturtleman]

Currently the code for stencil shadow volumes is broken and disabled. It doesn't draw anything.

[Calinou]

/cg_shadows 4 (only works with OpenGL 2) is a decent workaround in the meantime. It's based on shadowmaps, but without any filtering applied. The shadows have less of a tendency to fly in random directions as well (my largest pet peeve with /cg_shadows 2 – these would really benefit from a fixed angle option).