Async: Make tests Promise-aware

Fixes #632.
Ref #534.

~~I'm **not** loving how un-DRY the `Test#run` function is... but that's not _new_, only exacerbated by this PR.~~

**Updated:** This makes the `setup`, `teardown`, and `test` methods all aware that their return value may be a Promise in need of asynchronous resolution (`resolve`-ing).

Criticism or other suggestions welcomed, as usual.

cc: @domenic @stefanpenner
you can cut every lines above as these tests are now in [test/modules.js](https://github.com/jquery/qunit/blob/master/test/modules.js#L66-L141)