Description:
------------
If xpath->query is used in combination with namespaces in the xml document it produces a memory leak. The memory leak couldn't be identified with memory_get_usage. Only top could show us the raising memory usage.

Reproduce code:
---------------
#!/usr/local/apache2/bin/php
<?php 

$xml_str = '<?xml version="1.0" encoding="UTF-8"?>
            <items xmlns:a="http://www.example.org/" xmlns:b="http://www.example2.org/" xmlns:c="http://www.example3.org/" >
            <header>Item1</header>
            <item>Data</item>
            </items>
           ';

$xml_dom = DomDocument::loadXML( $xml_str );
$xpath = new domXPath( $xml_dom );   
for( $i=0; $i< 1000000; $i++ ) {
    $node_list = $xpath->query( '/*' );    
}

?>

Expected result:
----------------
The memory usage of the above code WITHOUT the namespace definition is 1.1% (using top). 

Actual result:
--------------
The memory usage of the above code WITH the namespace definition is starting by 1.1% and raising up to 7.4%(using top).