scd: Support PASSWD --clear for OpenPGP card.
* scd/app-openpgp.c (do_change_pin): Implement handling APP_CHANGE_FLAG_CLEAR.
It is specified in the specification version 3.1 or later. Some
version 2 cards (including Gnuk) support this feature. Any version 1
card has no support for this feature.
For CHVNO = 1, it clears for both of 81 and 82; That is, user's key
usages for signing and others (decryption and auth).
For CHVNO = 3, it clears for 83, admin key.
For CHVNO = 2, it clears 82; That is, user's key usages
others (decryption and auth).
- Signed-off-by: NIIBE Yutaka <email@example.com>