Convert dojo/on tests to Intern

This is a pull request for converting dojo/on tests to intern. When reading the DOH-based tests, it was difficult for me to ascertain what all the tests were doing and why, so I broke the tests into smaller pieces with clearer responsibilities.

Code coverage is hovering near 75% for all columns, but when I add an iOS 7 environment, coverage is in the high 80's (though none of the existing functional tests pass).

I've temporarily included the Intern [1.5 version bump](https://github.com/bryanforbes/dojo/pull/16) because one of the tests depends on an assert fix in 1.5.

The most controversial part of this pull request is that I included a fix to `on.emit` so that it returns a truthy value for `on.emit(target, { cancelable: false })` which is how `dispatchEvent` behaves. A comment in the syntheticDispatch function led me to believe this was the intended behavior. I would have created a dojo PR for this but didn't want to bother writing a DOH-based test for it. Let me know whether you agree with the fix and whether I should create a dojo PR for it.