Explicitly raise an exception in __cmp__ -- this clarifies that cmp()
is not supported on sets.  (Unfortunately, sorting a list of sets may
still return random results because it uses < exclusively, but for
sets that inly implements a partial ordering.  Oh well.)
diff --git a/Misc/NEWS b/Misc/NEWS
index 5f415d4..29411ec 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -78,6 +78,10 @@
 Library
 -------
 
+- The sets module now raises TypeError in __cmp__, to clarify that
+  sets are not intended to be three-way-compared; the comparison
+  operators are overloaded as subset/superset tests.
+
 - Bastion.py and rexec.py are disabled.  These modules are not safe in
   Python 2.2. or 2.3.