If a path is really unmerged, such as because it has been deleted and
also modifed, we cannot obtain a diff for it. Instead Git is sending
back '* Unmerged path <blah>' for file <blah>. We should display this
line as-is as our tag selecting switches don't recognize it.
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>