[session] Stop relying on _sessions to synchronize living session by doing what we currently do in pyramid. Also, attempt to synchronize CWUser's class sounds like a dark corner case handling that should be removed in favor of short lived user objects (beside it shouldn't occur except during migration).

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))