Query on Line 118 needs update to be compliant with PostgreSQL 8.3 backend

Current code results in following error:

* warning: pg_query() [function.pg-query]: Query failed: ERROR: for SELECT DISTINCT, ORDER BY expressions must appear in select list in /home/atlasproject/drupal-6.13/includes/database.pgsql.inc on line 139.
* user warning: query: SELECT DISTINCT n.nid as nid, m.plid as plid, m.mlid as mlid, n.title as title FROM book as b inner join menu_links as m ON b.mlid = m.mlid inner join node as n ON n.nid = b.nid WHERE m.plid = '341' AND n.status = 1 ORDER by m.weight, n.title, n.nid, m.plid, m.mlid in /home/atlasproject/drupal-6.13/sites/all/modules/booktree/booktree.module on line 118.weight

Line #118 which is now
$sql= "SELECT DISTINCT n.nid as nid, m.plid as plid, m.mlid as mlid, n.title as title

should become
$sql= "SELECT DISTINCT n.nid as nid, m.plid as plid, m.mlid as mlid, n.title as title, m.weight