agent: Ask specific SERIALNO for pksign/pkdecrypt.
* agent/call-scd.c (agent_card_serialno): Add DEMAND argument. * agent/command-ssh.c (card_key_available): Follow the change. * agent/learncard.c (agent_handle_learn): Likewise. * agent/divert-scd.c (ask_for_card): Use DEMAND argument.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>