Log: maintain selected file when changing commits to make examining historical differences easier

When trying to understand the history of a change, it's common for someone to open the log window and then click back and forth on different commits to see what changed in them.

Currently, when the user clicks on a commit, the differences pane in the log window switches to display the file that is at the top of the Files window based on the current sort order. This makes it cumbersome to switch back and forth between commits to see what happened to a particular file because, unless that file happens to be at the top of the sort order in each commit, the differences pane keeps jumping around between files.

As an example, attached are two screenshots of what happens to the view when I switch between two changelists, both of which contain the same file "DBExternalViewManagerImpl.inl". 

I click on first commit and select DBExternalViewManagerImpl.inl in the files window:

Then I click on next commit in log; DBExternalViewManagerImpl.inl does not remain selected in files window, and the contents of the differences pane therefore change:

What I think the behavior should be is:

1. the file selected in the current commit should remain selected when switching to another commit, so long as the other commit contains the same file.
2. when switching to a different commit that does not contain the same file, it should switch to either:
• The file that was selected most recently for this commit
• Or the file at the top of the sort order, if no file was previously selected for the commit

#1 is the most important. #2 would really help when skipping around through multiple changelists that may not all contain the same files, but I understand that it would require a tiny amount of state tracking and may not be as easy to implement as #1.

Thanks for considering this request.

(Note: I filed this several years ago via email and it was filed internally as SG-9991. Since I cannot find it here on userecho, I have assumed it got "lost" and am re-filing it)