Revert to jQuery 1.7.2 in https://gerrit.wikimedia.org/r/#/c/22555/

Guys we need something more tangible than "this blob with 2 million lines of code thrown together from 100+ different modules in browser X on wiki Y is slower".

A revert may do for the short term but not very sustainable, obviously.

There's half a dozen things that are significantly improved in performance in jQuery 1.8 over 1.7. We need to narrow it down, a lot.

• Bug 39961 has been marked as a duplicate of this bug. ***

Reverting to 1.7.2 has caused bug 40103

• Bug 40103 has been marked as a duplicate of this bug. ***

Reedy: Can this be closed? I don't see any other tickets left here, but I have no idea if you expect further regressions to be found.

1.8.1 has been integrated and released without issues.

We've since upgraded twice (to 1.8.2 and 1.8.3).