obshistory: only display each revision once in debugobshistory
When using a revision range, the same precursor could have been
displayed more than once. Use a cache to display each revision
only once.
It's a fix until we found the nicest way to display obs history.
This software was downloaded from
http://hg.netv6.net/evolve-main/
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'.