Description:
------------
When using DOMDocument::registerNodeClass for both DOMElement and DOMNode a 
DOMElement does nog get to be a child of the registered DOMNode class

Test script:
---------------
<?php
class MyDOMDocument extends DOMDocument {
	public function __construct($version = null, $encoding = null) {
		parent::__construct($version, $encoding);
		
		$this->registerNodeClass("DOMNode", "MyDOMNode");
		$this->registerNodeClass("DOMElement", "MyDOMElement");
        }
}

$dom = new MyDOMDocument();
$dom->loadXML("<root/>");

$parent_class_names = array();
$parent_class_name = get_class($dom->documentElement);
do {
    $parent_class_names[] = $parent_class_name;
} while($parent_class_name = get_parent_class($parent_class_name));

var_dump($parent_class_names);
?>

Expected result:
----------------
array (size=4)
  0 => string 'MyDOMElement' (length=12)
  1 => string 'DOMElement' (length=10)
  2 => string 'MyDOMNode' (length=9)
  3 => string 'DOMNode' (length=7)


Actual result:
--------------
array (size=3)
  0 => string 'MyDOMElement' (length=12)
  1 => string 'DOMElement' (length=10)
  2 => string 'DOMNode' (length=7)