* Add ListCreatingEvent and ListDeletingEvent.  These are sent before the
  operation actually occurs, whereas the previously added ListCreatedEvent and
  ListDeletedEvent are sent after the operation.  Specifically, this is
  necessary because request database deletion requires the IMailingList
  object, which is only available before the list is deleted.

* Add a handler to clear out the requests database for a mailing list, when
  the mailing list is about to be deleted.