message: parameter server append with overwrite func
diff: @@ -63,7 +63,7 @@ class ParameterServer(Params):
  val_self = self.store[key]
  val_other = p_server.store[key]
  if isinstance(val_self, ParameterServer) and isinstance(val_other, ParameterServer):
  - val_self.AppendParamServer(val_other)
  + val_self.AppendParamServer(val_other, overwrite=overwrite)
  elif not overwrite:
  logging.warning("Cannot append conflicting key '{}'!".format(key))
  if not key in self.store or overwrite:
  