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

clutter/clutter-bind-constraint.c

@@ -151,7 +151,7 @@ source_queue_relayout (ClutterActor          *source,
                        ClutterBindConstraint *bind)
 {
   if (bind->actor != NULL)
-    clutter_actor_queue_relayout (bind->actor);
+    _clutter_actor_queue_only_relayout (bind->actor);
 }
 
 static void