Index: ./includes/session.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/session.inc,v
retrieving revision 1.32
diff -u -r1.32 session.inc
--- ./includes/session.inc      31 Aug 2006 19:52:39 -0000      1.32
+++ ./includes/session.inc      4 Oct 2006 07:26:33 -0000
@@ -85,6 +85,12 @@
 function sess_regenerate() {
   $old_session_id = session_id();
   session_regenerate_id();
+
+  // destroy the session cookie on the client by setting the cookie to expire in the past (a negative value)
+  if (isset($_COOKIE[session_name()])) {
+    setcookie(session_name(), '', time()-42000, '/');
+  }
+
   db_query("UPDATE {sessions} SET sid = '%s' WHERE sid = '%s'", session_id(), $old_session_id);
 }