Function validate_config_vars() improperly validates multibyte strings

Function validate_config_vars() (adm/index.php) improperly validates multibyte strings.
This leads to, for example, incorrect validation of site description length when, say, ~244 unicode characters are entered.
The cause is use of strlen() instead of utf8_strlen() here:

			case 'string':

				$length = strlen($cfg_array[$config_name]);