Paint/pick all children, regardless of whether or not they lie within
the content_box. The previous behavior was that a child that was 99%
outside the box would be fully visible, but a child that was 100%
outside the box would be fully hidden. This is somewhat odd, and
doesn't match the behavior of the other St container classes, and at
any rate, the use of clutter_actor_get_allocation_box() for this
optimization was incorrect since it doesn't take into account
transformations (anchor point, rotation, etc) that might cause the
child to be drawn within the content_box anyway.

(For scrolled StBoxLayouts, drawing is still clipped to the
content_box, as before, but will now properly take transformations
into account as well.)