Responsive refresh hook at odds with double buffers

[benfrankel]

When the refresh_xxx method of an @Responsive attribute mutates a double buffer, its on_xxx_transition method is never called (this is a transition that fails to trigger the appropriate transition hook).

This is because refresh_xxx methods are called strictly after on_xxx_transition methods in the frame pipeline. Either refresh_xxx should be trusted not to mutate double buffers, or it should generate an error, or the frame pipeline has to be fixed.