Synchronize with latest JSON2

This pull request re-applies custom Pandell changes on top of latest JSON2 changes:

- Expose `JSON.stringifyJS` which is JavaScript-only serializer (as opposed to the native one that all modern browsers provide as `JSON.stringify`)
- If IE8 with known serialization bug (in its native serializer) is detected, we switch to using the JavaScript serializer instead (slower but doesn't serialize empty strings as `"null"` :wink: )