Make client's undo compatible with old and new ZODB tests.

old = 3.4.4 (Zope 2.8.x)
new = 3.10.0b5 (ZODB svn trunk)

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2341 71dcc9de-d417-0410-9af5-da40c76e7ee4

neo/client/app.py

@@ -974,7 +974,7 @@ class Application(object):
                         'transaction', oid)
                 undo_serial = None
             self._store(oid, current_serial, data, undo_serial)
-        return tid, oid_list
+        return tid, []
 
     def _insertMetadata(self, txn_info, extension):
         for k, v in loads(extension).items():