The implementation of _clutter_actor_set_default_paint_volume which
simply uses the actor's allocation to determine a paint-volume was
needlessly using the allocation rounded to integers by internally using
clutter_actor_get_allocation_geometry instead of
clutter_actor_get_allocation_box. This was introducing a lot of
instability into the paint-volume due to the way rounding was done.

The code has now been updated to use clutter_actor_get_allocation_box
so we are dealing with the floating point allocation instead.

Signed-off-by: Neil Roberts <neil@linux.intel.com>
Signed-off-by: Emmanuele Bassi <ebassi@linux.intel.com>