Rename gettext to cwgettext, use stdlib gettext cubicweb/gettext.py was a copy of Python 2.6's gettext.py with the context patch from bug https://bugs.python.org/issue2504 Instead of keeping that full copy, just inherit from gettext.GNUTranslations and add the context-related stuff.

option_group_changed('cleanup-session-time', 'web', 'main')