Poor code coverage in environments with spec-compliant native implementations

[ghost]

Istanbul currently reports that JSON 3 has 13.77% coverage. This is actually correct, since the native stringify and parse implementations are used in Node; however, this metric is also not very useful. I've merged d10/json3@a5e43925b7c8889e0d3d34f52d4082c758b58eff to squelch the Travis failures, but it would be wonderful to investigate how other polyfills measure code coverage.

[bnjmnt4n]

I think what we should do for this is to replace Node’s spec-compliant JSON implementation with a faulty one that doesn’t work correctly. We can then use Istanbul accurately to detect JSON3’s code coverage. @kitcambridge What do you think? If you’re fine with it I can experiment with this.