func (snap *ZoneSnapshot) StoreRecordsForSerial(zone string, serial int, records []*endpoint.Endpoint) {
	snap.serials[zone] = serial
	snap.endpoints[zone] = records
}
func (snap *ZoneSnapshot) StoreRecordsForSerial(zone string, serial int, records []*endpoint.Endpoint) {
	snap.serials[zone] = serial
	snap.endpoints[zone] = records
}
// StoreRecordsForSerial associates a result set with a (zone, serial)