- Loading non-binary string pickles checks for insecure
          strings. This is needed because cPickle (still)
          uses a restricted eval to parse non-binary string pickles.
          This change is needed to prevent untrusted
          pickles like::

            "S'hello world'*2000000\012p0\012."

          from hosing an application.

        - User-defined types can now support unpickling without
          executing a constructor.

          The second value returned from __reduce__ can now be None,
          rather than an argument tuple. On unpickling, if the second
          value returned from __reduce__ during pickling was None, then
          rather than calling the first value returned from __reduce__,
          directly, the __basicnew__ method of the first value returned
          from __reduce__ is called without arguments.