scd: Make the PIN cache robust against wrongdoing of gpg-agent.
* scd/app-openpgp.c (struct app_local_s): New field pincache. (cache_pin): Set it. (pin_from_cache): Consult it. * scd/app-piv.c (struct app_local_s): New field pincache. (cache_pin): Set it. (pin_from_cache): Consult it.
- Signed-off-by: Werner Koch <wk@gnupg.org>