t.i.task.Clock.advance should set the call.called attribute.

[ralphm]

If a DelayedCall produced by twisted.internet.task.Clock.callLater has its cancel() method called after its callback function has been called, the following exception is raised:

exceptions.ValueError: list.remove(x): x not in list

This is quite a cryptic error.

Setting call.called to 1 before calling the callback makes the cancel() call raise the proper AlreadyCalled exception.

[ralphm]

(In [18644]) Add timeout behaviour to xmpp iq requests and make t.i.Clock set call.called.

Author: ralphm Reviewer: exarkun Fixes #2218 and #2222