added pants/shirt layer rendering to GLSL shader, rather than calling it three times...

added pants/shirt layer rendering to GLSL shader, rather than calling it three times like before (which was very slow)
migrated GLSL light shader permutation selection (and correspondingly all parameter setup) into R_Shadow_RenderSurfacesLighting_Light_GLSL, this causes more setup overhead but allows specific optimization of non-colormapping and non-specular surfaces so this should be a speed gain overall

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@5936 d7cf8633-e32d-0410-b094-e92efae38249