Update lib/jquery.retryAjax.js

Fixed for JQuery 1.9.0 -
A few questions added to the code comments..
From Jquery website:
Deprecation Notice: The jqXHR.success(), jqXHR.error(), and jqXHR.complete() callbacks are deprecated as of jQuery 1.8. To prepare your code for their eventual removal, use jqXHR.done(), jqXHR.fail(), and jqXHR.always() instead.