[doc] Document the user_data dictionnary content

[debian] break old cubicweb-vcsfile We removed call_service's async argument, which it used.

[services] catch missing group early in register_user Better an assertion than a rql syntax error for such a programming error.

[services] rename register_user kwargs to cwuserkwargs They're attributes/relations for the created CWUser, this makes it clearer.

[services] don't hardcode 'users' group for register_user Let the caller choose which group the user should be in. Related to #3020639 Caveat: this is a possible security hole if untrusted values are allowed.

[sobjects/test] check that register_user properly sets user name and email address Related to #3020639

[server] Refactor Repository.register_user into a CubicWeb service (closes #3020639) [jcr: move commit to the caller; add item in release notes; fix NameErrors]

[migration] set a cnxset before process_script() Not pretty, but I don't have a better idea right now and this at least ensures migration scripts get run in the expected environment and can access sql stuff as before.

[server] make internal_cnx get and keep a connection to the db - internal_session worked that way - it's less surprising for users if their internal connections "just work", rather than having to deal with the cnxset when using low-level APIs Includes a backout of 3f62606c01a2 "[repo] Fix register_user" which is no longer needed. Depend on logilab-database 1.12.1 to avoid errors due to pointless check in python's sqlite3 binding.

[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.