* agent/agent.h (agent_ssh_key_from_file): New.
* agent/command-ssh.c (get_ssh_keyinfo_on_cards): New.
(ssh_send_available_keys): Loop on the GNUPG_PRIVATE_KEYS_DIR.
Support keys by agent_ssh_key_from_file.
(ssh_handler_request_identities): Move card key handling to
ssh_send_available_keys.
* agent/findkey.c (public_key_from_file): New.  Adding handling
for SSH.
(agent_public_key_from_file): Use public_key_from_file.
(agent_ssh_key_from_file): New.