* src/agent.h (struct key_info_s, key_info_t): Move to ...
* src/cert.h (struct key_info_s): here.
* src/agent.c (learn_status_cb): Set usage info.
(scute_agent_learn): Use "SCD LEARN" instead of "LEARN"
(struct pkdecrypt_parm_s): New.
(pkdecrypt_data_cb): New.
(pkdecrypt_inq_cb): New.
(pkdecrypt_parse_result): New.
(scute_agent_decrypt): New.
* src/cert-object.c (scute_attr_prv): Set decrypt flag.  Replace arg
'grip' by 'kinfo'.  Change callers.
* src/gpgsm.c (struct search_cb_parm): Replace 'grip' by 'kinfo'.
(scute_gpgsm_get_cert): Replace args 'grip' and 'certref' by 'kinfo'.
* src/slots.c (struct session): Add 'decryption_key'.  Change callers.
(slot_create_session): Init decryption_key.
(session_sign): Allow NULL for PSIGNATURE but still return the
required length.
(session_init_decrypt): New.
(session_decrypt): New.