overhauled vertex formats, now supports 100% interleaved arrays

overhauled vertex formats, now supports 100% interleaved arrays
rendering mode, reworked vertexbuffer management to be a more robust
system, added fully vertex buffered rendering options
(gl_vbo_dynamicvertex, gl_vbo_dynamicindex) which are off by default
(they seem to hurt fps in tests here)
centralized handling of "generic" mesh rendering (fixed function stuff)

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@10109 d7cf8633-e32d-0410-b094-e92efae38249