[BUGFIX beta] Prevent strict mode errors from superWrapper.

In Strict Mode accesing the global `window` is considered unsecure,
and will cause errors. This changes just guards against setting
properties on `window` (which throws an error).

[Here](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions_and_function_scope/Strict_mode#.22Securing.22_JavaScript) is what MDN has to say about "Securing" JavaScript.