g10: Select a secret key by checking availability under gpg-agent.
* g10/getkey.c (finish_lookup): Add WANT_SECRET argument to confirm by agent_probe_secret_key. (get_pubkey_fromfile, lookup): Supply WANT_SECRET argument.
- GnuPG-bug-id: T1967
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>