agent: handle SSH operation by KEYGRIP.
* agent/command-ssh.c (card_key_available): Supply KEYINFO argument. Call agent_card_readkey by KEYGRIP of KEYINFO. Don't use $AUTHKEYID, but IDSTR of KEYINFO. (ssh_handler_request_identities): Follow the change of card_key_available.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>