SF bug #668906: class browser raises AttributeError

The Py2.3 updates to the pyclbr module return both Class and Function
objects.  The IDLE ClassBrowser module only knew about Class and could
not handle objects which did not define "super".

Fixed by adding a guard.

Lib/idlelib/ClassBrowser.py

@@ -98,7 +98,7 @@ def listclasses(self):
         for key, cl in dict.items():
             if cl.module == name:
                 s = key
-                if cl.super:
+                if hasattr(cl, 'super') and cl.super:
                     supers = []
                     for sup in cl.super:
                         if type(sup) is type(''):