Patch Set 3:

- ACK now can open compare on untracked file
- I think CommitFileDiffViewer.showTwoWayFileDiff(final FileDiff d) shows how to open compare view with reusing the compare view (that's what is used when double clicking on a file entry in a commit's file list in History View when compare mode is enabled in order to bring up the compare view)
- for unstage support in jgit have a look at
 IndexDiffTest.removeFromIndex(String path)
I think this should do the trick