* g10/card-util.c (gen_kdf_data): Support single salt.
(kdf_setup): Can have argument for single salt.
* scd/app-openpgp.c (pin2hash_if_kdf): Support single salt.
--
Gnuk has "admin-less" mode. To support "admin-less" mode with KDF
feature, salt should be same for user and admin. Thus, I introduce a
valid use of single salt.
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>