Bind constraints: Don't force redraws on source relayout

When the source actor potentially changes size, that shouldn't
necessarily result in the target actor being redrawn - it should
be like when a child of a container is reallocated due to changes
in its siblings or parent - it should redraw only to the extent
that it is moved and resized. Privately export an internal function
from clutter-actor.c to allow getting this right.

https://bugzilla.gnome.org/show_bug.cgi?id=719367
Don't queue redraws when reallocating actor that haven't moved

When support for implicit animation of actor position was added,
the optimization for not queueing when allocating an actor back
to the same location was lost. This optimization is important
since when we are hierarchically allocating down from the top of
the stage we constantly reallocate the actors at the top of the
hierarchy back to the same place.

https://bugzilla.gnome.org/show_bug.cgi?id=719368