obslog: add header to the changeset description diff
This patch adds `diff -r <hash> -r <hash> <filename>` header to the output of
the changeset description diff which is shown using the --patch flag of obslog
command.
This fixes the label/color issue for description diff also.
This software was downloaded from
https://www.mercurial-scm.org/repo/evolve/
Copyright 2011 Peter Arrenbrecht <peter.arrenbrecht@gmail.com>
Logilab SA <contact@logilab.fr>
Pierre-Yves David <pierre-yves.david@ens-lyon.org>
Patrick Mezard <patrick@mezard.eu>
This software may be used and distributed according to the terms of the GNU
General Public License version 2 or any later version.
On Debian systems, the complete text of the GNU General Public License version
2 can be found in `/usr/share/common-licenses/GPL-2'.