include_once(config.local.php) instead of include()ing it

This should avoid problems with endless include loops like in
https://sourceforge.net/p/postfixadmin/bugs/367/


git-svn-id: https://svn.code.sf.net/p/postfixadmin/code/trunk@1830 a1433add-5e2c-0410-b055-b7f2511e0802

config.inc.php

@@ -574,7 +574,7 @@ $CONF['xmlrpc_enabled'] = false;
 // file (config.local.php) instead of editing this file and override some
 // settings there.
 if (file_exists(dirname(__FILE__) . '/config.local.php')) {
-    include(dirname(__FILE__) . '/config.local.php');
+    include_once(dirname(__FILE__) . '/config.local.php');
 }
 
 //