Description:
------------
Tested on PHP 5.1.3 -> 5.2.1

Using addAttribute() when referring to a child called "Host" causes PHP to return a CGI Error.

Reproduce code:
---------------
<?php
$string = <<<XML
<?xml version="1.0"?>
<Host enable="true">
 <Name>host.server.com</Name>
</Host>
XML;

$xml = simplexml_load_string($string);

$add = $xml->addChild('Host');
$add->Host->addAttribute('enable', 'true');
?>


Expected result:
----------------
Running it should add a child called "Host" and add the attribute "enable" with the value "true".

Actual result:
--------------
$add = $xml->addChild('Host') works fine.
Adding an attribute to a child named "Host" however, results in:
"The specified CGI application misbehaved by not returning a complete set of HTTP headers."