Incremental Crowd/Crowd synchronisation produces inconsistent events when a membership is deleted and recreated

When Crowd processes synchronisation events to send to clients it omits membership deletion events if that membership still exists (on the assumption that it's a shadowed membership change). However, if that membership is now present because it was recreated since the deletion then Crowd will still send the recreation event, which will now fail as that membership was never deleted.

Either the initial deletion should still be sent or the recreation should also be omitted.