The zeroes were added to fix http://bugs.jquery.com/ticket/4942 but those browsers are no longer supported.

For much improved consistency, jqXHR.abort() sets a default statusText of 'canceled' right until after beforeSend has been called (in which case it reverts to the default of 'abort'): now all early aborts have a statusText of 'canceled'.

$.ajax now always returns an object implementing the Promise interface. Fixes #10944. Unit tests amended.
For back-compat, in case of an early abort, callbacks passed in the options are not called (while subsequent callbacks attached to the returned Promise are).
For early abort triggered by returning false in beforeSend, statusText is "canceled".

Makes Deferred implementation truly Promise/A compliant. Unit tests amended. Actually few changes required in jQuery's own source and we gained 8 bytes minified gzipped \o/.

TestSwarm hasn't been happy since this commit, and everyone deserves to be happy.

This reverts commit 318d47b7.

Makes sure start is always called with default context and no arguments. Should stop FF from acting up. Hopefully, this ugly patch can be removed in the future.

Makes parseXML act like parseJSON when given an empty or non-string input: now returns null rather than throwing an exception. Incidently fixes #10527. Unit tests added.

Fixes #11264 or rather seriously limits the risk of global ajaxSettings screwing with script loading in domManip. Gotta love globals and sneaky dependencies. Unit test added.

Fixes #11426: getting the responseText of an xhr should be tried/caught because of IE's inability to give access to binary data. Unit test added.

No more php/js logic duplication. Ensures modules are still loaded separately when using "file:" protocol (makes debugging much easier, /kiss @rwaldron). Ensures test iframes will use the same jquery as specified in the main document. Known issue: chrome will cringe at cross-frame access using file: protocol, apparently chrome sees this as cross-domain... go figure.

Supplements #11356 and fixes unit test failures in FF 3.6.

When the browser window isn't visible, setTimeouts have 1-second granularity.