Add run-loop assertions.
Merge pull request #135 from rwjblue/add-run-loop-assertion

Add run-loop assertions.
Fixup test-helpers/index.

* Use `asserts` instead of `assertions` (that is what is used internally in the helpers).
* Make `callForEach` a function generator (so that `this.asserts`
  works).
* Fix typo in `Composite` prototype.
* MOAR TESTS!!