Ajax: use anchor tag for parsing urls

This PR changes the Ajax URL parsing from using a regex to using an anchor tag. This should be simpler and more reliable.

Fixes https://github.com/jquery/jquery/issues/1875
/cc @dmethvin
Note sure if this will help, but here's a very similar solution with a giant comment about IE: https://github.com/angular/angular.js/blob/master/src/ng/urlUtils.js#L25