Description:
------------
In SimpleXML, when deleting attributes via 'unset', attributes having the same namespace as the element (or some such wrong namespace) are deleted rather than the non-prefixed one which is the one actually appearing in the 'array' (or not appearing--it can still be deleted if it does not appear).

Reproduce code:
---------------
$str=<<<DONE
<?xml version="1.0" encoding="utf-8"?>
<root
	xmlns="http://localhost/a"
	xmlns:ns="http://localhost/a"
	xmlns:other="http://localhost/b"
>
<elem attr="abc"/>
<elem ns:attr="abc"/>
<elem other:attr="abc"/>
<ns:elem attr="abc"/>
<ns:elem ns:attr="abc"/>
<ns:elem other:attr="abc"/>
<other:elem attr="abc"/>
<other:elem ns:attr="abc"/>
<other:elem other:attr="abc"/>
</root>
DONE;

$xml = simplexml_load_string($str);
foreach ($xml->elem as $elem) {
	unset($elem['attr']);
}
foreach ($xml->children('http://localhost/a')->elem as $elem) {
	unset($elem['attr']);
}
foreach ($xml->children('http://localhost/b')->elem as $elem) {
	unset($elem['attr']);
}
echo $xml->asXML();


Expected result:
----------------
<?xml version="1.0" encoding="utf-8"?>
<root xmlns="http://localhost/a" xmlns:ns="http://localhost/a" xmlns:other="http://localhost/b">
<elem/>
<elem ns:attr="abc"/>
<elem other:attr="abc"/>
<ns:elem/>
<ns:elem ns:attr="abc"/>
<ns:elem other:attr="abc"/>
<other:elem/>
<other:elem ns:attr="abc"/>
<other:elem other:attr="abc"/>
</root>


Actual result:
--------------
<?xml version="1.0" encoding="utf-8"?>
<root xmlns="http://localhost/a" xmlns:ns="http://localhost/a" xmlns:other="http://localhost/b">
<elem/>
<elem/>
<elem other:attr="abc"/>
<ns:elem attr="abc"/>
<ns:elem/>
<ns:elem other:attr="abc"/>
<other:elem attr="abc"/>
<other:elem ns:attr="abc"/>
<other:elem/>
</root>