Better support for file renames in pull request diff views

In git if you rename a file with "git mv" then it appears to understand that a file was renamed and will only show content changes when you do a "git diff".

It would be nice if the pull request diff view could understand this for file renames, currently it just shows the entire old filename as removed and the new filename as added, which is not very useful when trying to see a diff of a file that was renamed and changed slightly.

I can provide specific links to PR's in my team repo if you need some examples.

thanks!