agent: Improve support for externally cached passwords.
* agent/call-pinentry.c (PINENTRY_STATUS_PASSWORD_FROM_CACHE): New constant. (pinentry_status_cb): Add it to *FLAGS if PASSWORD_FROM_CACHE was provided. (agent_askpin): Pass "OPTION allow-external-password-cache" to the pinentry. Always pass SETKEYINFO to the pinentry. If there is no stable identifier, then use "--clear". If the password is incorrect and PINENTRY_STATUS_PASSWORD_FROM_CACHE is set in *PINENTRY_STATUS, then decrement PININFO->FAILED_TRIES.
- Signed-off-by: Neal H. Walfield <neal@g10code.com>