Description:
------------
When calling asXML() to a cloned element, the php segfaults. I've got no debug information, but the bug is easy to reproduce. I had this problem with PHP 5.2.0 and PHP 5.1.6. With PHP 5.1.2 everything is OK. 

The xml file is just an example - this happens with every xml file I tried!

Reproduce code:
---------------
alexiev-home:~/tests# cat SimpleXML.xml
<?xml version="1.0" encoding="utf-8" ?>
<test>

</test>
alexiev-home:~/tests# cat SimpleXML.php
<?php
$root = simplexml_load_file('SimpleXML.xml');
$clone = clone $root;
var_dump($root);
var_dump($clone);
echo $clone->asXML(); // Segfault here
?>


Expected result:
----------------
object(SimpleXMLElement)#1 (1) {
  [0]=>
  string(2) "

"
}
object(SimpleXMLElement)#2 (1) {
  [0]=>
  string(2) "

"
}
string(55) "<?xml version="1.0" encoding="utf-8"?>
<test>

</test>
"


Actual result:
--------------
object(SimpleXMLElement)#1 (1) {
  [0]=>
  string(2) "

"
}
object(SimpleXMLElement)#2 (1) {
  [0]=>
  string(2) "

"
}
Segmentation fault