Description:
------------
When importing nodes and their children via DOMDocument::importNode, the method 
will introduce the "default" namespace prefix. Herein lies a bug that will trigger 
if the namespace prefix "default" is already assigned (even if not applied to any 
element) within the children of the imported node.

Test script:
---------------
<?php
$aDOM=DOMDocument::loadXML(<<<EOXML
<A xmlns="http://example.hilses.de/A">
	<B>
		<C
			xmlns="http://example.hilses.de/C"
			xmlns:default="http://example.hilses.de/Z" />
	</B>
</A>
EOXML
);

$bDOM=new DOMDocument();
$node = $bDOM->importNode($aDOM->getElementsByTagNameNS('http://example.hilses.de/A','B')->item(0), true);
$bDOM->appendChild($node);

echo $bDOM->saveXML()."\n";
?>

Expected result:
----------------
<?xml version="1.0"?>
<B xmlns="http://example.hilses.de/A" xmlns:default="http://example.hilses.de/C">
		<default:C />
</B>

or even better:

<?xml version="1.0"?>
<B xmlns="http://example.hilses.de/A">
		<C xmlns="http://example.hilses.de/C"/>
</B>

Actual result:
--------------
<?xml version="1.0"?>
<B xmlns="http://example.hilses.de/A" xmlns:default="http://example.hilses.de/C">
	<default:C xmlns="http://example.hilses.de/C" 
xmlns:default="http://example.hilses.de/Z"/>
</B>


(see how C is put into the ".../Z" namespace now instead of ".../C", since 
namespace prefix declarations are valid for the element in which they are 
defined!)