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

classes/NoticeWrapper.php

@@ -35,7 +35,7 @@ class NoticeWrapper extends Notice {
     public $is_local;                        // tinyint(1)  
     public $source;                          // varchar(32)  
 
-    var $notices = NULL;
+    var $notices = null;
     var $i = -1;
     
     function __construct($arr) {