Description:
------------
When a class is registered to a DOMDocument via the registerNodeClass method, the assigned class is used to instance the return object from the DOMDOcument. However, the construct method of that class is not called. 

Test script:
---------------
class SillyTestClass extends DOMElement{
    public $foo=null;
    public function __construct($name,$value=null,$namespace=null){
        echo "calling child construct....";
        $this->foo="bar";
        parent::__construct($name,$value,$namespace);
    }
    public function sayHello(){
        echo "Why, hello there!";
    }
}

$doc=new DOMDocument();
$doc->registerNodeClass('DOMElement','SillyTestClass');
$doc->loadHTML("<div><h1>Sample</h1></div>");
//THIS WORKS! CUSTOM CLASS BEING USED
$doc->documentElement->firstChild->sayHello();

//THIS IS STILL NULL:( Never set by construct, no message saying construct was called either  
echo $doc->documentElement->firstChild->foo; 

Expected result:
----------------
output "calling child construct..." //printed from child _construct
output "Why, hello there!" //printed from child method sayHello()
output "bar" //the value of child property after being assigned in constructor

Actual result:
--------------
//only the sayHello() method fires; construct doesn't happen
Why, hello there;