Added gl_renderbuffers CVAR that disables render buffers
Added patch shader support to FShaderProgram
Added OpenGL 2 fallback support to render buffers
- removed gl_vid_compatibility. With the bump to 1.4 no hardware requiring this flag is supported anymore.
- disabled 16 bit framebuffers for the same reason. As a conseqence all code for rendering without stencil could also be removed.