gpg: Improve the code to decrypt using PIV cards.
* g10/call-agent.c (agent_scd_keypairinfo): Add arg 'keyref'. * g10/keygen.c (ask_algo): Adjust. * g10/skclist.c (enum_secret_keys): Request the keyref directly.
This improves commit ec6a6779236a89d4784a6bb7de0def9cc0f9e8a4 to avoid
looping over all keypairinfos. This way scdaemon does not need to
compute all the keypairinfos for all keys of a card. This patch is
possible due the enhanced READKEY command in scdaemon.
- Signed-off-by: Werner Koch <wk@gnupg.org>