Fix breakage with zodbpickle >= 2

Starting from zodbpickle 2 its binary class does not allow users to set
arbitrary attributes and so

	binary._pack = bytes.__str__

fails with

	TypeError: can't set attributes of built-in/extension type 'zodbpickle.binary'

-> Fix it by explicitly checking for binary type on encoding instead of
setting binary._pack

See slapos@27f574bc for pre-history.

/cc @jerome

neo/client/__init__.py

@@ -13,13 +13,6 @@
 ##############################################################################
 
 def patch():
-    # For msgpack & Py2/ZODB5.
-    try:
-        from zodbpickle import binary
-        binary._pack = bytes.__str__
-    except ImportError:
-        pass
-
     from hashlib import md5
     from ZODB.Connection import Connection
 

neo/lib/protocol.py

@@ -18,6 +18,12 @@ import threading
 from functools import partial
 from msgpack import packb
 
+# For msgpack & Py2/ZODB5.
+try:
+    from zodbpickle import binary
+except ImportError:
+    class binary: pass # stub, binary should not be used
+
 # The protocol version must be increased whenever upgrading a node may require
 # to upgrade other nodes.
 PROTOCOL_VERSION = 2
@@ -52,6 +58,8 @@ def Unpacker():
 
     iterable_types = set, tuple
     def default(obj):
+        if isinstance(obj, binary):
+            return obj.__str__()
         try:
             pack = obj._pack
         except AttributeError: