Poor stream handling

[MikkelHJuul]

If for some reason an error is returned when trying to send a message for *Many-RPCs and *Range-RPCs the error is logged and the request is not cancelled. This may lead to issues.

go func() {
   for kv := range out {
		if err := sender.Send(kv); err != nil {
			log.Warn(err)
		}
	}
	cancel()
} ()

should be handled using "golang.org/x/sync/errgroup".