cache: introduce an abstract class for cache we can upgrade incrementally Right now each class implements their own mechanism for validation, and update. We start introducing abstract class to ultimately allow more unification of the cache code. The end goal of this series is to introduce a cache for some obsolescence property, not to actually implement the cache. However, taking advantage of adding a new cache to introduce the abstract class seems like a win. This code was headed for core during the 4.3 cycle but never made it there. So we starts with a copy in the evolve repository.

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'.