Undo :meth:`set_signal_handlers`.

        Not only must this be done on shutdown, but after every fork
        call too.

def clear_signal_handlers(self):
        '''Undo :meth:`set_signal_handlers`.

        Not only must this be done on shutdown, but after every fork
        call too.

        '''
        signal.signal(signal.SIGABRT, self.old_sigabrt)
        signal.signal(signal.SIGINT, self.old_sigint)
        signal.signal(signal.SIGPIPE, self.old_sigpipe)
        signal.signal(signal.SIGTERM, self.old_sigterm)