[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).

[bdist_wheel]
universal = 1

[check-manifest]
ignore =
  debian
  debian/*
  cubicweb.spec
  __pkginfo__.py