Description:
------------
Since 5.1.3 you cannot copy a dom object. References still work. The implementation of the xml extension seam to have changed.

Reproduce code:
---------------
Since 5.1.3 the following code does not work anymore:

<?php

$dom1 = new DomDocument('1.0', 'UTF-8');

$xml = '<foo />';
$dom1->loadXml($xml);

print "<xmp>\n".$dom1->saveXML()."</xmp>\n";

$node = clone $dom1->documentElement;

$dom2 = new DomDocument('1.0', 'UTF-8');
$dom2->appendChild($dom2->importNode($node->cloneNode(true), TRUE));

print "<xmp>\n".$dom2->saveXML()."</xmp>\n";

$dom3 = clone $dom1;

print "<xmp>\n".$dom3->saveXML()."</xmp>\n";

?>

Expected result:
----------------
<?xml version="1.0"?>
<foo/>

<?xml version="1.0"?>
<foo/>

<?xml version="1.0"?>
<foo/>


Actual result:
--------------
&lt;?xml version="1.0"?&gt; &lt;foo/&gt;
Warning: DOMNode::cloneNode() [function.DOMNode-cloneNode]: Couldn't fetch DOMElement in /www/content/
spielzeug/xslt/513.php on line 13

Warning: DOMDocument::importNode() expects parameter 1 to be DOMNode, null given in /www/content/
spielzeug/xslt/513.php on line 13

Warning: DOMNode::appendChild() expects parameter 1 to be DOMNode, null given in /www/content/
spielzeug/xslt/513.php on line 13
&lt;?xml version="1.0" encoding="UTF-8"?&gt;
Warning: DOMDocument::saveXML() [function.DOMDocument-saveXML]: Couldn't fetch DOMDocument in /www/content/
spielzeug/xslt/513.php on line 19