Add license revisioning clause.

LICENSE

 The OpenLDAP Public License
 
-  Version 2.0.1, 21 December 1999
-  Copyright 1999, The OpenLDAP Foundation, Redwood City, California, USA.
+  Version 2.1, 29 February 2000
+  Copyright 1999-2000, The OpenLDAP Foundation, Redwood City, California, USA.
   All Rights Reserved.
 
 Redistribution and use of this software and associated documentation
@@ -30,6 +30,11 @@ of the OpenLDAP Foundation.
 5. Due credit should be given to the OpenLDAP Project
 (http://www.openldap.org/).
 
+6. The OpenLDAP Foundation may revise this license from time to
+time.  Each revision is distinguished by a version number.  You
+may use the Software under terms of this license revision or under
+the terms of any subsequent license revision.
+
 THIS SOFTWARE IS PROVIDED BY THE OPENLDAP FOUNDATION AND CONTRIBUTORS
 ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
 NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND