--isort sorts imports even if they were not edited

[akaihola]

The problem with applying isort modifications "surgically" is in the fact that isort may (and often does) change the order of lines.

Could we consider all changes by isort as one contiguous diff chunk, and apply it if any line in edited_linenums falls inside that chunk? Is there an edge case where isort only modifies part of the import lines, and a user edit happens to an import outside that part? I can't see a problem there. The important thing is that either all or none of the isort modifications are applied.