Issue the given Assuan command and return a Deferred that will fire
        with the response.

def issueCommand(self, command, *args):
        """
        Issue the given Assuan command and return a Deferred that will fire
        with the response.
        """
        result = Deferred()
        self._dq.append(result)
        self.sendLine(b" ".join([command] + list(args)))
        return result