Update the rake backups task to include Mercurial repositories
This is the first version of a working backup process including Mercurial- repositories.
This commit contains several hacks that will need to be cleaned at one time:
- Find a clean way to get / compute the webdir.conf disk path
- Find a way to don't backup the sync_hook.py.
- Find a way to don't backup the hg-git git repository. It seems hg-git doesn't like to start-over without this repository. When trying to push after restoring, it fails with "Parent SHA-1 not present in Gitrepo".