debug: make add_client() more generic

https://bugzilla.gnome.org/show_bug.cgi?id=710017
debug: stop using tp_list_connection_names()

Make the code more symetric.

https://bugzilla.gnome.org/show_bug.cgi?id=710017
debug: factor out helpers

https://bugzilla.gnome.org/show_bug.cgi?id=710017
use list_names_cb to find MC

Make the code more symetric.

https://bugzilla.gnome.org/show_bug.cgi?id=710017