'Issue the given command via the cftp client. Return a C{Deferred} that
fires when the server returns a result. Note that the C{Deferred} will
callback even if the server returns some kind of error.
@param command: A string containing an sftp command.
@return: A C{Deferred} that fires when the sftp server returns a
result. The payload is the server\'s response string.'

def runCommand(self, command):

    self._expectingCommand = defer.Deferred()
    self.clearBuffer()
    if isinstance(command, unicode):
        command = command.encode('utf-8')
    self.transport.write((command + '\n'))
    return self._expectingCommand
