Ah, webapp doesn't start listening until all the startup code has run?

If webapp did for example start listening as it's own startup callback (instead of waiting until everyone else's startup had run), then we'd have the race condition, and throwing an error would just mean that some early requests for the manifest would fail.

But since it waits, we don't need either the autoUpdateVersion callback pattern *or* Meteor.startup(), because the connect handler here won't be called until webapp starts listening.