Object __proto__ can be hijacked

[winstliu]

Running CSON.readFile on the following CSON results in the callback object's __proto__ being hijacked:

'__proto__':
  toString: 1

Any calls to the object's .toString() method will fail as toString is now an object.

This also has the side effect of preventing season from properly returning __proto__ keys (which can be useful in, for example, snippets).