core: New public enum gpgme_keyorg_t.

* src/gpgme.h.in (gpgme_keyorg_t): New.
* src/keylist.c (parse_keyorg): New.
(keylist_colon_handler): Set key->ORIGIN.

This finally set the key origin value form data supplied by recent gpg
versions.

• Signed-off-by: Werner Koch <wk@gnupg.org>