launch_daemon: We can now talk to the authentication manager.

* When creating the port of the registrar's authentication manager, we
  now set it manually, so that the user/group functions work.
* This allows LaunchDaemon::_StartSession() to set up the user, and
  groups as needed.

headers/private/libroot/user_group.h

@@ -89,6 +89,7 @@ public:
 
 
 port_id		get_registrar_authentication_port();
+void		set_registrar_authentication_port(port_id port);
 status_t	send_authentication_request_to_registrar(KMessage& request,
 				KMessage& reply);