Description:
------------
When extending from SplFileObject and overwriting the constructor, it is not 
easily possible to override the parent one because for the last parameter $context 
one can not provide an optional default.

Therefore it requires (somewhat needles) if-branched code only to deal with the 
$context not passed case when calling the parents constructor.

It would be nice if $context does accept NULL then if I do not want to use any 
context but need to specify the parameter.

Test script:
---------------
<?php

class Myfile extends SplFileObject
{
    public function __construct($file_name, $open_mode = "r", $use_include_path = FALSE, $context = NULL) {
        $this->levels = new Levels();
        parent::__construct($file_name, $open_mode, $use_include_path, $context);
    }
}

$file = new MyFile(__FILE__);

Expected result:
----------------
It should not give any warning or error.

Actual result:
--------------
Warning: Missing argument 4 for Myfile::__construct(), called in [pointing to the 
line "$file = new MyFile(__FILE__);"]  and defined in [pointing to the line 
"public function __construct($file_name, $open_mode = "r", $use_include_path = 
FALSE, $context = NULL) {"]