'Remove a deferred d from our waiting list, as the deferred has been
canceled.
Note: We do not need to wrap this in a try/except to catch d not
being in self.waiting because this canceller will not be called if
d has fired. release() pops a deferred out of self.waiting and
calls it, so the canceller will no longer be called.
@param d: The deferred that has been canceled.'

def _cancelAcquire(self, d):

    self.waiting.remove(d)
