vbo: Try to reuse the same VAO more often for successive dlists.

vbo: Try to reuse the same VAO more often for successive dlists.

The change tries to catch more opportunities to reuse the same set
of VAO's when building up display lists. Instead of checking the
offset with respect to the beginning of the vertex buffer object
the change tries to apply this same optimization with respect to the
previous display list node.

Reviewed-by: Brian Paul <brianp@vmware.com>
Signed-off-by: Mathias Fröhlich <Mathias.Froehlich@web.de>