Description:
------------
The return value from callback in xmlrpc_server_register_introspection_callback() isn't freed.

Memory leak found using --enable-debug.

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

$options = array ();
$request = xmlrpc_encode_request ("system.describeMethods", $options);
$server = xmlrpc_server_create();

function foo() { }

xmlrpc_server_register_introspection_callback ($server, 'foo');

$options = array ('output_type' => 'xml', 'version' => 'xmlrpc');
xmlrpc_server_call_method ($server, $request, NULL, $options);


Expected result:
----------------
No mem. leak.

Actual result:
--------------
[Fri Jul 18 11:48:38 2008]  Script:  '/home/felipe/public_html/bug.php'
/home/felipe/php5_2/ext/xmlrpc/xmlrpc-epi-php.c(885) :  Freeing 0x085DC198 (16 bytes), script=/home/felipe/public_html/bug.php
[Fri Jul 18 11:48:38 2008]  Script:  '/home/felipe/public_html/bug.php'
/home/felipe/php5_2/Zend/zend_operators.c(543) :  Freeing 0x085DC1D8 (1 bytes), script=/home/felipe/public_html/bug.php
=== Total 2 memory leaks detected ===