St: fix container paint volumes

St: fix container paint volumes

If a container is not clip-to-allocation, then its get_paint_volume()
needs to include the paint volumes of all of its children, since they
(or their children) may paint outside the container's allocation.

Also, if the superclass get_paint_volume() returns FALSE, then the
subclass should return FALSE too.

https://bugzilla.gnome.org/show_bug.cgi?id=655812