g10: Change ask_curve so that it can be used outside.
* g10/call-agent.h (struct key_attr): New. * g10/keygen.c (ask_curve): Return const char *. No allocation. (quick_generate_keypair): Follow the change. (generate_keypair, generate_subkeypair): Likewise. (parse_algo_usage_expire): Return const char *.
This change is intended for using ask_curve from card-util.c.
- Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>