gpg: Try Signer's User ID sub-packet with --auto-key-retrieve.
* g10/packet.h (PKT_signature): Add field 'signers_uid'. * g10/parse-packet.c (parse_signature): Set this field. * g10/free-packet.c (free_seckey_enc): Free field. (copy_signature): Copy field. * g10/mainproc.c (akl_has_wkd_method): New. (check_sig_and_print): Extend NEWSIG status. If WKD is enabled try to locate a missing key via the signature's Signer's User ID sub-packet. Do this right before trying a keyserver lookup.
- Signed-off-by: Werner Koch <wk@gnupg.org>