A few Reporter Fixes

I'm not sure if these are still necessary but this Pull Request:
- adds `_$blanket` to the ignored globals list
- calls `originalReporter` with the correct `this`
- adds `suiteURL` and `testURL` methods which are expected by HTMLReporter

These were added to get tests working on <https://github.com/philschatz/css-coverage.js> and <https://github.com/philschatz/octokit.js>