- removed old immediate mode path for generating stencils.
- fixed: Plane height changes only updated the first buffered vertex for the respective plane.
- fixed: GLPortal::DrawPortalStencil must apply the render state before drawing anything.
- convert skybox rendering to use the buffer interface.
- removed gl_usevbo CVAR because with recent code changes it has become useless. If GL_ARB_buffer_storage is present, buffers will always be used.
- use buffer based rendering for dynamic light pass and horizon portals.