Suppress protocol 3 pickle tests on Python2.

src/ZODB/_compat.py

@@ -14,7 +14,12 @@
 
 try:
     # Python 2.x
-    from cPickle import Pickler, Unpickler, dump, dumps, loads
+    from cPickle import Pickler
+    from cPickle import Unpickler
+    from cPickle import dump
+    from cPickle import dumps
+    from cPickle import loads
+    from cPickle import HIGHEST_PROTOCOL
     IMPORT_MAPPING = {}
     NAME_MAPPING = {}
     _protocol = 1
@@ -22,6 +27,7 @@ except ImportError:
     # Python 3.x: can't use stdlib's pickle because
     # http://bugs.python.org/issue6784
     import zodbpickle.pickle
+    HIGHEST_PROTOCOL = 3
     from _compat_pickle import IMPORT_MAPPING, NAME_MAPPING
 
     class Pickler(zodbpickle.pickle.Pickler):

src/ZODB/tests/testUtils.py

@@ -122,6 +122,8 @@ class TestUtils(unittest.TestCase):
     def test_get_pickle_metadata_w_protocol_3_class_pickle(self):
         from ZODB.utils import get_pickle_metadata
         from ZODB._compat import dumps
+        from ZODB._compat import HIGHEST_PROTOCOL
+        if HIGHEST_PROTOCOL >= 3:
             pickle = dumps(ExampleClass, protocol=3)
             self.assertEqual(get_pickle_metadata(pickle),
                             (__name__, ExampleClass.__name__))