Patch Set 4: I would prefer that you didn't submit this

(1 inline comment)

I still find problems:
- The comparison of the staged changes is not with HEAD but with the parent of HEAD (see inline comment in GitCacheCompareInput)
- The compare editor for a file with both index and working dir changes shows conflicts in red
- When a file is deleted I see the file with a normal decorator; the right hand side of the compare editor is just empty. I can see nowhere that the file is deleted.