Make an XML-RPC call to the server. This method will automatically
        authenticate the call with self.api_key, if that is set.

        returns: deferred that when fired returns a dict with data from this
                 XML-RPC call.

def call(self, action, payload):
        """
        Make an XML-RPC call to the server. This method will automatically
        authenticate the call with self.api_key, if that is set.

        returns: deferred that when fired returns a dict with data from this
                 XML-RPC call.
        """
        if self.api_key:
            payload['Bugzilla_api_key'] = self.api_key
        d = self.proxy.callRemote(action, payload)
        d.addErrback(self._parse_errback)
        return d