- Small documentation improvements.

database/updates.inc

 <?php
 // $Id$
 
+// SCHEMA and SCHEMA_MIN represent the minimum and maximum N modulename_update_N.
+// Update SCHEMA when a new update function is added.  Update SCHEMA_MIN when old
+// update functions are removed.
 function system_version($type) {
   switch ($type) {
     case SCHEMA: