'Establish a passive data connection (i.e. client connecting to
server).
@param ignored: ignored
@return: L{Deferred.addCallback}'

def _makeDataConnection(self, ignored=None):

    d = self.client.queueStringCommand('PASV')
    def gotPASV(responseLines):
        (host, port) = ftp.decodeHostPort(responseLines[(-1)][4:])
        cc = protocol.ClientCreator(reactor, _BufferingProtocol)
        return cc.connectTCP('127.0.0.1', port)
    return d.addCallback(gotPASV)
