[DX] adding error messages to {ResultSet,ActionsRegistry}.possible_actions Try to make it more accessible, when we first encountered these errors it it didn't made any sense to us.

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