make the reference to older versions of the documentation a link

to the right page on python.org

Doc/ext/newtypes.tex

@@ -16,8 +16,9 @@ get started.
 The way new types are defined changed dramatically (and for the
 better) in Python 2.2.  This document documents how to define new
 types for Python 2.2 and later.  If you need to support older
-versions of Python, you will need to refer to older versions of this
-documentation.
+versions of Python, you will need to refer to
+\ulink{older versions of this documentation}
+      {http://www.python.org/doc/versions/}.
 \end{notice}
 
 \section{The Basics