Do auto-correct one cop at a time if necessary

And make sure that each cop doesn't try to correct two things in the
same location.
Make sure offenses are always sorted

The output of offenses should be in order of location, even in the
auto-correct case when they are discovered in a loop of investigating
and writing corrections.
Merge pull request #819 from jonas054/fix_autocorrect_problem

Fix autocorrect problem