add license information to the gemspec

This way we can get it when using rubygems.org API
Some IE7 browsers do not implement withCredentials on
their XHR object and always setting it explicitly
(even if setting to null) causes those browsers to
fail.
Merge branch 'master' of https://github.com/jordimassaguerpla/jquery-rails into jordimassaguerpla-master
Updated to latest jquery_ujs.js
Added note to README about jquery versions in CHANGELOG.
Updated to jquery 1.9.1.
Version 2.2.1