Make get_line_changed_regions accessible in diffutils.
Review Request #5494 — Created Feb. 18, 2014 and submitted
get_line_changed_regions is going to be used outside of ChunkGenerator.
This is a simple change that pulls it out of there and into diffutils,
where it can be accessed as public API.
Made use of this in a different call site.
Also, this functionality still works on the diff viewer.
Unit tests pass.
