GUI-293: Flag XHR requests from AngularJS with the proper header to let Pyramid handlers properly leverage the requests.is_xhr flag.
Note: This needs to be explicitly enabled for all $http.get/$http.post operations in Angular per issue 2366 - https://github.com/angular/angular.js/issues/2366
GUI-293: Handle invalid token or session timeout errors in XHR calls.
Fix broken auth unit tests.
Remove duplicate string template.
Merge pull request #118 from eucalyptus/GUI-293

GUI-293: Better handling of 403 errors via XHR calls.