The only use we had for RAS_StorageIM was to render derived meshes using
Blender's mesh drawing. This is now handled as a special case in
RAS_OpenGLRasterizer instead of in RAS_StorageIM.
We are now left with RAS_StorageVA and RAS_StorageVBO. At the moment
vertex arrays are still the default since our vertex array with display
lists implementation is still much faster than our VBO code in a lot of
cases. As we improve our VBO code, we can drop vertex arrays since
Blender's minimum OpenGL version is being bumped up to 2.1, which
supports VBOs.