This is due to us now having multiple parallel compilations (feature tests and `type="text/traceur"`) coexisting at the same time, right?

If we stop using `type="text/traceur"` and move to a system where everything is immediately run to the end after compile, we can ignore the unique id problem. Except for the case where you expect newly declared vars to be undefined. And those cases don't involve generated ids (I'm pretty sure all our generated ids are initialized).