Date.prototype.toJSON is not generic

[petermichaux]

The ECMAScript 5.1 specification requires that the Date.prototype.toJSON method be generic and that the this object only needs to have a toISOString method. The Date.protototype.toJSON polyfill of json2.js is not generic.

http://es5.github.com/#x15.9.5.44

[douglascrockford]

Please let me know if this ever manifests as a real problem.