'Add a pair of callbacks (success and error) to this L{Deferred}.
These will be executed when the \'master\' callback is run.
@return: C{self}.
@rtype: a L{Deferred}'

def addCallbacks(self, callback, errback=None, callbackArgs=None, callbackKeywords=None, errbackArgs=None, errbackKeywords=None):

    assert callable(callback)
    assert ((errback is None) or callable(errback))
    cbs = ((callback, callbackArgs, callbackKeywords), ((errback or passthru), errbackArgs, errbackKeywords))
    self.callbacks.append(cbs)
    if self.called:
        self._runCallbacks()
    return self
