editting hunks in diff-mode

[Jens Petersen]

Jonathan reported a couple of issues a while back with editting in
diff-mode, which last I checked were still present in cvs emacs:

 diff-mode corrupts diff when it is edited
 http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=64702

 diff-mode can't find a hunk
 http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=64707

Perhaps it would be nice to fix these when there is time.

Jens