* agent/agent.h (agent_key_from_file): Change the declaration.
* agent/findkey.c (agent_key_from_file): Return timestamp.
* agent/pkdecrypt.c (agent_pkdecrypt): Follow the change.
* agent/pksign.c (agent_pkdecrypt): Likewise.
* agent/command.c (cmd_passwd, cmd_export_key): Likewise.
(cmd_keytocard): Use timestamp in private key file in "Created:".