Improve sync_test, add time to SyncNote
Improve sync_test, add time to SyncNote

- sync.go: Add time of message to SyncNote
- various: Set the new Time field
- sync_test.go: Add clarifying comments
- sync_test.go: Clean up some test failure messages
- sync_test.go: Remove named return args on newSyncTest
- sync_test.go: IPv4/v6 distinction not used, so remove arg from newLocalTCPListener
- sync.go: Minor refactor of sync session creation into own method
- sync.go: Cleanup of infinite loop + one-case select -> range over ticker

google/seesaw