Add index entries for new-style/old-style class.

Doc/ref/ref3.tex

@@ -1068,7 +1068,11 @@ in case of multiple inheritance.
 This manuel is not up-to-date with respect to new-style classes.  For now,
 please see \url{http://www.python.org/doc/newstyle.html} for more information.
 
-The plan is to eventually drop old-style classes, leaving only the semantics of new-style classes.  This change will probably only be feasible in Python 3.0.
+The plan is to eventually drop old-style classes, leaving only the semantics of
+new-style classes.  This change will probably only be feasible in Python 3.0.
+\index{class}{new-style}
+\index{class}{classic}
+\index{class}{old-style}
 
 %=========================================================================
 \section{Special method names\label{specialnames}}