agent: Add KEYTOCARD command.
* agent/agent.h (divert_writekey, agent_card_writekey): New. * agent/call-scd.c (inq_writekey_parms, agent_card_writekey): New. * agent/command.c (cmd_keytocard, hlp_keytocard): New. (register_commands): Add cmd_keytocard. * agent/divert-scd.c (divert_writekey): New.