This patch attempts to do to cPickle what Guido did
   for pickle.py v 1.50. That is: save_global tries
   importing the module, and fetching the name from the
   module. If that fails, or the returned object is not
   the same one we started with, it raises a
   PicklingError. (All this so pickling a lambda will
   fail at save time, rather than load time).