fix ZopeUndo.Prefix decode on python 2

setup.py

@@ -33,6 +33,7 @@ tests_require = [
     'random2',
     'mock',
     'msgpack-python',
+    'ZopeUndo',
 ]
 
 classifiers = """

src/ZEO/asyncio/marshal.py

@@ -157,7 +157,7 @@ def find_global(module, name):
 def server_find_global(module, name):
     """Helper for message unpickler"""
     try:
-        if module != 'ZopeUndo.Prefix':
+        if module not in ('ZopeUndo.Prefix', 'copy_reg', '__builtin__'):
             raise ImportError
         m = __import__(module, _globals, _globals, _silly)
     except ImportError as msg:

src/ZEO/tests/test_marshal.py

+import unittest
+from ZEO.asyncio.marshal import encode
+from ZEO.asyncio.marshal import pickle_server_decode
+from ZopeUndo.Prefix import Prefix
+
+
+class MarshalTests(unittest.TestCase):
+
+    def testServerDecodeZopeUndoFilter(self):
+        # this is an example of Zope's 
+        args = (0, 20, {'user_name': Prefix('test')})
+        # test against repr because Prefix __eq__ operator
+        # doesn't compare Prefix with Prefix but only
+        # Prefix with strings. see Prefix.__doc__
+        self.assertEqual(
+            repr(pickle_server_decode(encode(*args))),
+            repr(args)
+        )
+
+
+def test_suite():
+    suite = unittest.TestSuite()
+    suite.addTest(unittest.makeSuite(MarshalTests))
+    return suite
+