Problem with patch for ajax timeout reporting

Problem with patch for ajax timeout reporting

Currently it appears not to be possible to know, in the ajax error
callback, if the request has failed due to a timeout, versus some
other reason. Knowing this is important for implementation of a good
UI, which wants to be able to say more than "timeout or other error".
I propose having the "status" parameter contain string "timeout" when
the error is due to a timeout. 

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