Switch to pickle format 3 so bytes and unicodes are not smashed.

Will have to introduce a new protocol version for the new format.

src/ZEO/_compat.py

@@ -17,8 +17,21 @@ import sys
 
 PY3 = sys.version_info[0] >= 3
 
-# Pickle support
-from ZODB._compat import Pickler, Unpickler, dump, dumps, loads
+if PY3:
+    from pickle import Pickler, Unpickler as _Unpickler, dump, dumps, loads
+    class Unpickler(_Unpickler):
+        # Py3: Python 3 doesn't allow assignments to find_global,
+        # instead, find_class can be overridden
+
+        find_global = None
+
+        def find_class(self, modulename, name):
+            if self.find_global is None:
+                return super(Unpickler, self).find_class(modulename, name)
+            return self.find_global(modulename, name)
+else:
+    # Pickle support
+    from cPickle import Pickler, Unpickler, dump, dumps, loads
 
 # String and Bytes IO
 from ZODB._compat import BytesIO
@@ -37,3 +50,4 @@ try:
     from cStringIO import StringIO
 except:
     from io import StringIO
+

src/ZEO/zrpc/marshal.py

@@ -33,7 +33,7 @@ def encode(*args): # args: (msgid, flags, name, args)
     if PY3:
         # XXX: Py3: Needs optimization.
         f = BytesIO()
-        pickler = Pickler(f, 1)
+        pickler = Pickler(f, 3)
         pickler.fast = 1
         pickler.dump(args)
         res = f.getvalue()