Temporarily remove uncaughtException listeners.

As I mentioned in #93, Grunt's `uncaughtException` listeners fire before Karma gets a chance to stop the browsers it started.

The only fix that I can think of is removing Grunt's listners for as long as Karma is running. That way, Karma can gracefully handle a framework raising an error or the user pressing Ctrl-c.

I made a small gist to reproduce the problem: <insert link>