return a list of other invalidated boxes when reconciling layout

Instead of indicated that something has changed and outer boxes have to
adapt, we return a list of the boxes that need to adapt. This can e.g.
be used by table cells that span over several rows, to indicate which
rows need to be reconciled.

Signed-off-by: Florian Thienel <florian@thienel.org>
26 files changed