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

actions/subedit.php

@@ -21,7 +21,7 @@ if (!defined('LACONICA')) { exit(1); }
 
 class SubeditAction extends Action {
 
-    var $profile = NULL;
+    var $profile = null;
 
     function prepare($args) {