Dovecot promotes the use of BLF-CRYPT as a hashing scheme [1].
However, as not all libc-crypt() implementations support this scheme,
use the implementation added in a previous commit.
Also, update the references to the dovecot implementation and a small
test case for testing the blowfish implementation.
[1] https://doc.dovecot.org/configuration_manual/authentication/password_schemes/Fixes#4958