Deprecate domains

ref https://github.com/iojs/io.js/issues/66

Also, I did notice that `domain.dispose()` is deprecated but missing a deprecation message. So it includes a commit which fixes it. Please inform me if you want it as a separate pull request.

I've also changed two test assertions. I belive usage of domain in `lib/repl.js` was swallowing the assert errors and that those are currently broken.
This is just me being paranoid, but could we use `.once` here?