password longer than 13 chars. This protects against the GNU crypt() which
does not return NULL if the algorithm is not supported, and return a DES
encrypted password.
SHA256, and SHA512 exactly (not only the first 3/6 chars).
* libmisc/salt.c (SHA_salt_rounds): Set rounds to the specified
prefered_rounds value, if specified.
* src/gpasswd.c, libmisc/salt.c: Fix compilation warnings (use
size_t for lengths).
* src/chpasswd.c, src/chgpasswd.c: Add missing parenthesis.
