Completely overhaul the tests.

- Use zuul for automating the HTML page generation and browserifying.
  - `npm test` now runs `npm run node-test`, which is just Mocha in Node, and `npm run phantomjs-test`, which uses zuul to run in PhantomJS.
  - `npm run browser-test` uses zuul to set up a server on 8080 that you can test at; it re-bundles the files each request.

- Add settable `asap.onerror` to which uncaught errors can be forwarded.
  - This allows trapping full error objects, not just error messages (`window.onerror` can only do the latter).
  - It also fixes all browser-compat problems with `window.onerror`.
  - It allows us to test asap directly, instead of a wrapped version of asap whose errors are trapped and put elsewhere.

- Rewrote tests to be straightforward and imperative.
  - No more custom microsyntax for writing the tests.
  - No more 187 lines of prelude before actually getting to the tests.
  - Tests now set up a task graph explicitly, then compare the call order and/or exception order to the expected order.

- Added a very rudimentary browser shim for the domain module.
  - Uses `asap.onerror` to record any errors.
  - Allows the test code to look the same in both Node and the browser.
  - Centralizes browser and Node.js divergences in a single file and single abstraction.
  - Gives us a place for the Node 0.8 bugfix (which also uses `asap.onerror`).

- Removed expect.js dependency in favor of the built-in assert module.
Test-only `asap.setOnError` instead of public `asap.onerror`.