Fix for SF bug #485678.

slot_tp_descr_set(): When deleting an attribute described by a
descriptor implemented in Python, the descriptor's __del__ method is
called by the slot_tp_descr_set dispatch function.  This is bogus --
__del__ already has a different meaning. Renaming this use of __del__
is renamed to __delete__.

Misc/NEWS

@@ -4,6 +4,12 @@ XXX Release date: ??-Dec-2001 XXX
 
 Type/class unification and new-style classes
 
+- The "delete attribute" method of descriptor objects is called
+  __delete__, not __del__.  In previous releases, it was mistakenly
+  called __del__, which created an unfortunate overloading condition
+  with finalizers.  (The "get attribute" and "set attribute" methods
+  are still called __get__ and __set__, respectively.)
+
 Core and builtins
 
 Extension modules