Fixes
-Fix conformance issues in r_fbo
-Fixes projected shadow issues with VR mode
-Fix for issue with framebuffer retaining last rendered scene during cut scenes/loading
Initial work towards moving to OpenGL 2.0 as a minimum version
-Remove code dependency on GLU
-Remove enumeration of GL_SGIS_generate_mipmap
-Remove enumeration of several extensions guaranteed by OpenGL 2.0
Move to OpenGL 2.0 conformant two sided stencil code path