passwords: use crypt_sha1 when saving passwords

passwords: use crypt_sha1 when saving passwords

Previously the crypt function was used to save passwords.
It has a number of drawbacks including only using the first
8 characters of the user-provided password.

Instead use a compatible implementation of the NetBSD
__crypt_sha1 function instead.  This allows all characters
of the password to be used and is more resistant to cracking
than the DES-based crypt.  The produced values should be
100% compatible with those output by NetBSD's __crypt_sha1().

Existing crypt passwords will continue to recognized but
any new or updated passwords will use crypt_sha1.