* Bug fix: Switch grade-books fires an ajax request and unless aborted would render the response from the server.  This may not have been noticeable because the plugin will render the responses in the order in which they were sent and so eventually the right gradebook would be rendered.  This fix kills the unnecessary and outstanding ajax requests.

git-svn-id: https://plugins.svn.wordpress.org/an-gradebook/trunk@1029776 b8457f37-d9ea-0310-8a92-e5e31aec5664