Description:
------------
PHP crashes when trying to call xmlrpc_set_type with a correctly formatted ISO8601 datetime string from the date() function. 

Note that if you specify a datetime string without the +/-00:00, it will work.
If you specify the timezome information (as the constant DATE_ISO8601 does), php will crash.


Reproduce code:
---------------
// this code breaks
$d = date(DATE_ISO8601);
xmlrpc_set_type($d, 'datetime');
echo xmlrpc_encode_request('method.call', array('date' => $d));


//working code
$d = '2008-01-01 20:00:00';
xmlrpc_set_type($d, 'datetime');
echo xmlrpc_encode_request('method.call', array('date' => $d));

Expected result:
----------------
<methodCall>
<methodName>method.call</methodName>
<params>
 <param>
  <value>
   <struct>
    <member>
     <name>date</name>
     <value>
      <dateTime.iso8601>20080101T20:00:00</dateTime.iso8601>
     </value>
    </member>
   </struct>
  </value>
 </param>
</params>
</methodCall>

Actual result:
--------------
*** stack smashing detected ***: php terminated
Aborted (core dumped)