cPickle.c, load_build(): Taught cPickle how to pick apart

the optional proto 2 slot state.

pickle.py, load_build():  CAUTION:  Noted that cPickle's
load_build and pickle's load_build really don't do the same
things with the state, and didn't before this patch either.
cPickle never tries to do .update(), and has no backoff if
instance.__dict__ can't be retrieved.  There are no tests
that can tell the difference, and part of what cPickle's
load_build() did looked accidental to me, so I don't know
what the true intent is here.

pickletester.py, test_pickle.py:  Got rid of the hack for
exempting cPickle from running some of the proto 2 tests.

dictobject.c, PyDict_Next():  documented intended use.

Lib/test/pickletester.py

@@ -728,12 +728,6 @@ class AbstractPickleTests(unittest.TestCase):
             self.assertEqual(y.abc, 666)
             self.assertEqual(x.__dict__, y.__dict__)
 
-# XXX Temporary hack, so long as the C implementation of pickle protocol
-# XXX 2 isn't ready.  When it is, move the methods in TempAbstractPickleTests
-# XXX into AbstractPickleTests above, and get rid of TempAbstractPickleTests
-# XXX along with the references to it in test_pickle.py.
-class TempAbstractPickleTests(unittest.TestCase):
-
     def test_newobj_list_slots(self):
         x = SlotList([1, 2, 3])
         x.foo = 42
@@ -745,6 +739,7 @@ class TempAbstractPickleTests(unittest.TestCase):
         self.assertEqual(x.foo, y.foo)
         self.assertEqual(x.bar, y.bar)
 
+
 class MyInt(int):
     sample = 1