Automatically retry failed AJAX requests to reduce annoying error messages

I have added an option (enabled by default) to automatically retry all failed AJAX requests up to 5 times.
Comment requests are not retried to avoid duplicates. Post button is fixed instead.
Errors on *like* and *skip* requests which occur because the request actually succeeds are removed and the page is updated to reflect actual changes.
Additionally the mouse cursor now indicates if requests are in progress, so you know when it is safe to leave the page.