shadow volume rendering still very incomplete, but works mostly

shadow volume rendering still very incomplete, but works mostly
committing this before I add 3D textures to the texture manager
(alert: this is the last version of the stencil shadow rendering that will work with TNT class hardware (and not well), 3D textures will be required and will not work on TNT class... sorry.  vertex just looks too horrible)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@2496 d7cf8633-e32d-0410-b094-e92efae38249