[web] on logout, use the base_url argument of build_url instead of hacking the request to get proper url. This fix a bug on site with http/https versions: the session cookie is badly removed on logout
""" CW - nevow/twisted client
:organization: Logilab
:copyright: 2001-2010 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
"""