code: def as_backfill_cron_app(cls):
      
      #----------------------------------------------------------------------
      def main(self, function=None):
          return super(cls, self).main(
              function=function,
              once=False,
          )
      cls.main = main
      cls._is_backfill_app = True
      return cls
docs: a class decorator for Crontabber Apps.  This decorator embues a CronApp
      with the parts necessary to be a backfill CronApp.  It adds a main method
      that forces the base class to use a value of False for 'once'.  That means
      it will do the work of a backfilling app.