Description:
------------
according to http://www.w3.org/TR/REC-xml-names/ ,
both 
   <root xmlns="...">
and 
   <root xmlns:ns="...">
are valid,

xpath->query() will fail with the first case.


Reproduce code:
---------------
<?php
$xml=<<<end
<?xml version="1.0"?>
<root xmlns="urn:schemas-upnp-org:device-1-0">
<child />
</root>
end;

$doc=new DomDocument();
$doc->loadXML($xml);

$xpath=new DomXpath($doc);

$query='/root';

$result=$xpath->query($query);
echo $result->length;


Expected result:
----------------
string '1'

Actual result:
--------------
string '0'