'Notify the any replication listeners that there\'s a new event'

def notify_replication(self):

    with PreserveLoggingContext():
        deferred = self.replication_deferred
        self.replication_deferred = ObservableDeferred(defer.Deferred())
        deferred.callback(None)
    for cb in self.replication_callbacks:
        preserve_fn(cb)()
