extending MIT krb5 string-to-key API

[Ken Raeburn]

Our current string-to-key API consists of these two functions:

    krb5_error_code KRB5_CALLCONV
        krb5_c_string_to_key
        (krb5_context context, krb5_enctype enctype,
                        const krb5_data *string, const krb5_data *salt,
                        krb5_keyblock *key);

    #ifdef KRB5_OLD_CRYPTO
    krb5_error_code KRB5_CALLCONV krb5_string_to_key
            (krb5_context context,
                    const krb5_encrypt_block * eblock,
                    krb5_keyblock * keyblock,
                    const krb5_data * data,
                    const krb5_data * salt);
    #endif

Neither has a hook for the new "string-to-key parameters" we need to
add to implement AES, unless we want to do ugly things with the
krb5_context.

Unless there are objections or better suggestions, I'll add this new
function to krb5.h and krb5_32.def.  (Is the current Mac export list
in the krb5 tree or the kfm tree?)  I don't plan to update the
OLD_CRYPTO API.

    krb5_error_code KRB5_CALLCONV
    krb5_c_string_to_key_with_params(krb5_context context,
                                     krb5_enctype enctype,
                                     const krb5_data *string,
                                     const krb5_data *salt,
                                     const krb5_data *params,
                                     krb5_keyblock *key);

Since we've cast the existing API into stone now, I won't remove or
change krb5_c_string_to_key, but it's now the wrong thing for any code
to call that wants to get the user's real Kerberos key.  Comments?

Ken