Collection checks in modification callbacks.

Never let the selection be updated if the deleted or modified list
coming in is empty or doesn't contain any element in the selection.
Add FRX clear after the transaction is closed.
Move FRX flag reset to base class.
Delete elements then modify elements.
Remove unused ElementMapping class.

This class was throwing exceptions that were causing the document
modification events to fail, and it is unused.
More comments and remove early bailout.
Do a set comparison to check whether to actually update the set.
Add a visual debugging tool for forcereexecute.
Remove set comparison

This keeps FRX from being set during modifications which you actually
want in order to do things like update geometry.
Don't set FRX on faces when unrelated elements are deleted.
Fix one test.

Force this transaction closed to ensure document modification is fired.
Comment out the FRX debug border.