replace NULL with null

Another global search-and-replace update. Here, I've replaced the PHP
keyword 'NULL' with its lowercase version. This is another PEAR code
standards change.

darcs-hash:20081223192129-84dde-4a0182e0ec16a01ad88745ad3e08f7cb501aee0b.gz

scripts/jabberqueuehandler.php

@@ -35,7 +35,7 @@ set_error_handler('common_error_handler');
 
 class JabberQueueHandler extends XmppQueueHandler {
 
-    var $conn = NULL;
+    var $conn = null;
 
     function transport() {
         return 'jabber';