Actually, related to this comment/change here and https://github.com/jehiah/pynsq/commit/a197264c3e9b12406236ae0e030a086be9e209b1, what do you think about clients sending or not sending an `AUTH` command by checking the version of the `nsqd` they're connected to (they get this back from the `IDENTIFY` command).

We could then restore the original response semantics.