* g10/trustdb.c: Move a function and some definitions around.
(user_utk_list): Rename to trusted_key_list.  Change all users.
(any_trusted_key_seen): New.
(tdb_register_trusted_key): Set it here.  Handle the new value "none".
(verify_own_keys): Do not delete a trusted key from the trustdb if a
trusted-key option was not used.