Description:
------------
Trying to do an XPath search on a SimpleXML object fails 
when the XML document contains namespaces.

Expected result:
----------------
The object should automatically register any prefixes 
defined using xmlns:foo="http://www.example.com" syntax 
in the document and also use any namespaces added 
using registerNS().

Actual result:
--------------
The following patch http://www.trachtenberg.com/patches/
simplexml_xpath_ns_patch.txt fixes both issues. (Note 
that the default namespace *is not* automatically 
registered, but that's a fault of the XPath spec, not 
the code. So you still need to manually register it.)