jsHint: Conform to jQuery jsHint style guide

QUnit doesn't currently conform to our [jsHint-related style guide](http://contribute.jquery.org/style-guide/js/#linting). This PR fixes it.

BTW, I wanted to add the `es3` option in tests since we should check if we didn't break oldIE but I was blocked on this bug: https://github.com/jshint/jshint/issues/1508

I accidentally submitted a PR from the `master` branch so I'm resubmitting it. The previous one was #524.