[krbdev.mit.edu #6031] krb needs better realm lookup logic

[Mark.Phalan@Sun.Com via RT]

This patch implements a heuristic to determine the realm name from the
dns domain name of a host.

The algorithm is:

    domain = fqdn;
    while (domain.label_count > 2) {
        domain = pop_label(domain);
        realm = domain2realm(domain); /* for ASCII: toupper() */
        if (lookup_kdcs(realm) > 0)
            break;
        realm = NULL;
    }

    return (realm);

The patch as attached makes libresolv specific calls (as thats what
OpenSolaris uses).