'Call L{_sendError} or L{_sendFailure}, depending on whether C{fail}
represents an L{Error} subclass or not.
@param fail: The failure.
@param requestID: The request ID.'

def _sendFailureOrError(self, fail, requestID):

    if (fail.check(Error) is None):
        self._sendFailure(fail, requestID)
    else:
        self._sendError(fail, requestID)
