Added additional username check in form files.

Till Brehm

2014-08-13 3ee67a99739154fa5fab3a041edabc14415d4e70

 interface/web/sites/lib/lang/en_shell_user.lng

@@ -31,4 +31,5 @@
$wb['invalid_system_user_or_group_txt'] = 'Invalid system user or group';
$wb['directory_error_regex'] = 'Invalid directory';
$wb['shell_error_regex'] = 'Invalid shell';
$wb['invalid_username_txt'] = 'Invalid Username';
?>