[server/session] make commit/rollback obey ensure_cnx_set Inside the ensure_cnx_set context manager, commit and rollback aren't allowed to dispose of the cnxset.

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances