gpg: Add dedicated error code for PGP-2 keys.
* g10/parse-packet.c (parse_key): Return GPG_ERR_LEGACY_KEY for PGP2 keys. * g10/import.c (read_block): Simplify by checking GPG_ERR_LEGACY_KEY. * g10/getkey.c (lookup): Silence error message for PGP-2 keys. * common/util.h (GPG_ERR_LEGACY_KEY): Add replacement for older libgpg-error.
- Signed-off-by: Werner Koch <wk@gnupg.org>