major refactoring of database dump/restore: * new hooks server_backup/server_restore called to allow cubes to add custom stuff to backup * each source may be backuped/restored * new --restore-all option to restore to restore everything, not only the system database (still the default behaviour)

# cube's specific schema
"""

:organization: Logilab
:copyright: 2001-2009 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
"""