Converting a Japanese Zenkaku(Full-width) login username to Hankaku(Half-width)

Students sometimes make login mistakes by typing their usename with Japanese Zenkaku(Full-width).
We can avoid this mistake by adding one line to login/index.php as below.

File:
login/index.php

Line:
123

[ before ]
if ($frm and isset($frm->username)) { // Login WITH cookies

$frm->username = trim(core_text::strtolower($frm->username));

[ after ]
if ($frm and isset($frm->username)) { // Login WITH cookies

$frm->username = mb_convert_kana($frm->username, 'a', 'utf-8');
$frm->username = trim(core_text::strtolower($frm->username));