def as_backfill_cron_app(cls):
<EOL>def main(self, function=None):<EOL><INDENT>return super(cls, self).main(<EOL>function=function,<EOL>once=False,<EOL>)<EOL><DEDENT>cls.main = main<EOL>cls._is_backfill_app = True<EOL>return cls<EOL>
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.