Description:
------------
DOMNode's getAttributeNodeNS method does not return xmlns* nodes.

[test.xml]

<?xml version="1.0" encoding="utf-8" ?>
<root xmlns="http://ns" xmlns:ns2="http://ns2">
    <ns2:child />
</root>

getAttributeNodeNS("http://www.w3.org/2000/xmlns/", "ns2") should return a node, as does getAttributeNode("xmlns:ns2").

Test script:
---------------
$xml=new DOMDocument();
$xml->load("test.xml");
$de = $xml->documentElement;
$ns2 = $de->getAttributeNodeNS("http://www.w3.org/2000/xmlns/", "ns2");
if ($ns2 == NULL) {
  echo 'namespace node does not exist.' . "\n";
} else {
  echo 'namespace node prefix=' . $ns2->prefix . "\n";
  echo 'namespace node namespaceURI=' . $ns2->namespaceURI . "\n";
}


Expected result:
----------------
namespace node prefix=ns2
namespace node namespaceURI=http://ns2


Actual result:
--------------
namespace node does not exist.