This isn't officially compatible with the oldest version of Node that
Jasmine supports, but it works. If it stops working, we can always disable
linting in CI builds on older Node versions.
* De-duplication now happens in core, not in reporters. This ensures that
the console doesn't get flooded.
* Stack traces are opt-out, not opt-in.
* The current runnable is not reported or logged for certain deprecations
where it's irrelevant.
* HtmlReporter shows stack traces in expandable widgets.
* Env#deprecated and Env#deprecatedOnceWithStack are merged.
