This change updates djblets to use jQuery 1.11. This also brings in the

jQuery-migrate plugin, which provides some compatibility implementations for

features which were removed from core jQuery.
The biggest changes within remove some compatibility-shims for older browsers

(notably IE8, which we haven't supported in a while). Other changes involve

some changes to .attr() vs .prop(), and a test to make sure we don't try to

append to nonexistant parts of the DOM (which is only a problem when running

js-tests).

Ran reviewboard js-tests.
Grepped through the javascript code and audited against the list of

  backwards-incompatible changes in jQuery 1.9 (1.10 and 1.11 are pretty

  trivial in terms of incompatible changes).