We have bent the originally documented semantics a bit so now where we
say "Queueing a new layout automatically queues a redraw as well" it
might be clearer to say "Queuing a new layout implicitly queues a redraw
as well if anything in the layout changes".
This should be close enough to the original semantics to not cause any
problems.
Without this change then we we fail to take advantage of clipped redraws
in a lot of cases because queuing a redraw with priv->needs_allocation
== TRUE will automatically be promoted to a full stage redraw since it's
not possible to determine a valid paint-volume.
Also queuing a redraw here will end up registering a redundant clipped
redraw for the current location, doing quite a lot of redundant
transforms, and then later when re-allocated during layouting another
queue redraw would happen with the correct paint-volume.
