Defer "changed" methods

[joneit]

The following should be able to be called multiple times, similar to repaint(), while deferring and collapsing all calls until the end of the thread:

• behaviorChanged Does one of the following:
• behaviorShapeChanged Recalculates scrollbars, followed by...
• behaviorStateChanged Recalculate rects of visible cells, followed by a call to repaint()

Right now the two recalc operations are performed on every call. For this reason we have always tried only to make such calls near end of thread, sometimes omitting calls where logically needed to avoid multiple recalcs but sometimes no doubt incurring multiple recalcs needlessly