implemented r_shadow_culltriangles cvar (on by default), this improves lighting perfo...

implemented r_shadow_culltriangles cvar (on by default), this improves lighting performance by reducing the amount of geometry to render, it does not add any additional cpu w
ork because similar forms of culling were already used on shadow casting triangles (which are now replaced by this), this just applies the same already computed culling to the lighting as well as the shadowing

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@6927 d7cf8633-e32d-0410-b094-e92efae38249