Fix #1321 Multipage doesn't work if portal.php is renamed

Fix #1321 Multipage doesn't work if portal.php is renamed
I think
```php
$file_name = THIS_SCRIPT;
$file_name_real = my_strtolower(basename($portal_url));
if($file_name_real != THIS_SCRIPT)
{
	$file_name = $file_name_real;
}
```
is same as
```php
$file_name = my_strtolower(basename($portal_url));
```