X Switch ZODB5 to use protocol=1

It works, at least on Python2.

src/ZODB/_compat.py

@@ -11,13 +11,14 @@
 # FOR A PARTICULAR PURPOSE
 #
 ##############################################################################
-from zodbpickle import binary  # noqa: F401 import unused
+#from zodbpickle import binary  # noqa: F401 import unused
+binary = bytes
 import sys
 from six import PY3
 
 IS_JYTHON = sys.platform.startswith('java')
 
-_protocol = 3
+_protocol = 1
 
 if not PY3:
     # Python 2.x

src/ZODB/tests/testSerialize.py

@@ -145,7 +145,7 @@ class SerializerTestCase(unittest.TestCase):
         pickle = serialize.ObjectWriter().serialize(top)
         # Make sure the persistent id is pickled using the 'C',
         # SHORT_BINBYTES opcode:
-        self.assertTrue(b'C\x04abcd' in pickle)
+        #self.assertTrue(b'C\x04abcd' in pickle) # disabled: we set protocol=1
 
         refs = []
         u = PersistentUnpickler(None, refs.append, BytesIO(pickle))
@@ -154,7 +154,7 @@ class SerializerTestCase(unittest.TestCase):
 
         self.assertEqual(refs, [['w', (b'abcd',)]])
 
-    def test_protocol_3_binary_handling(self):
+    def _test_protocol_3_binary_handling(self): # disabled: we set protocol=1
         from ZODB.serialize import _protocol
         self.assertEqual(3, _protocol)  # Yeah, whitebox
         o = PersistentObject()