Description:
------------
I enable and disable ignore_user_abort a few times during the execution but if the user aborts the request while the code is in a section that ignores it, it (of course) ignores it. But when I call ignore_user_abort(false) it doesn't check whether it was already aborted.

I think it would be useful to check whether we are already aborted when disabling the ignoring.

Test script:
---------------
It could also be accomplished with:

ignore_user_abort(true);
// critical section
ignore_user_abort(false);
if(connection_aborted()) {
  exit;
}