Description:
------------
When using insert_before($node,NULL) to insert a DOM element as the last child of some other element, insert_before never returns (and does not throw an error). 

This call will work, if $node is unlinked before. The documentation of insert_node, however, says that unlinking is not required.

See example code below.

Reproduce code:
---------------
<?php

$doc = domxml_open_mem("<foo><bar/></foo>");
$dom = domxml_open_mem("<outer><inner/></outer>");
$root = $doc->document_element();
$node = $dom->document_element();
//$node->unlink_node(); // uncomment this to work
$root->insert_before($node,NULL);
echo $doc->dump_mem();

?> 

Expected result:
----------------
Ideally:

<foo><bar/><outer><inner/></outer></foo>

If it is desired that the user has to explicitly unlink the node before inserting it, it would be nice to have an error message. insert_before should not hang.

Actual result:
--------------
insert_before does not return. The page is never sent to the client. No error message is given.