Update link to PythonWare library page.

Doc/lib/libundoc.tex

@@ -16,8 +16,8 @@ effort spent.
 \item[\module{Tkinter}]
 --- Interface to Tcl/Tk for graphical user interfaces; Fredrik Lundh
 is working on this one!  See
-\citetitle[http://www.pythonware.com/library/]{An Introduction to
-Tkinter} at \url{http://www.pythonware.com/library/} for on-line
+\citetitle[http://www.pythonware.com/library.htm]{An Introduction to
+Tkinter} at \url{http://www.pythonware.com/library.htm} for on-line
 reference material.
 
 \item[\module{Tkdnd}]