func (cd Codec) AddMulti(c context.Context, items []*Item) error {
	return cd.set(c, items, pb.MemcacheSetRequest_ADD)
}
func (cd Codec) AddMulti(c context.Context, items []*Item) error {
	return cd.set(c, items, pb.MemcacheSetRequest_ADD)
}
// AddMulti is a batch version of Add.
// appengine.MultiError may be returned.