[Fix #1374] Always auto-correct one cop at a time

The only way to guarantee that two cops don't destroy the code by doing simultaneous changes, is to save the file after letting one cop to its corrections, and then parse it again before doing any more corrections.

Performance will suffer a little bit, but I'm not worried about that. Correctness matters much more, of course.

I think there are some fixes done earlier that are no longer necessary after this change. That's less important, though. We can look at those later.