_reduce(): Avoid infinite recursion in the pickler when self.__class__

doesn't have the _HEAPTYPE flag set, e.g. for time.struct_time and
posix.stat_result.

This fixes the immediate symptoms of SF bug #496873 (cPickle /
time.struct_time loop), replacing the infinite loop with an exception.

Lib/copy_reg.py

@@ -53,6 +53,8 @@ def _reduce(self):
     if base is object:
         state = None
     else:
+        if base is self.__class__:
+            raise TypeError, "can't pickle %s objects" % base.__name__
         state = base(self)
     args = (self.__class__, base, state)
     try: