Setting dates using toString() so they work on ci servers.

Currently the `setValue` method accepts a value and calls `toJSON` on it before it is stored. Unfortunately, jasmine headless webkit can not properly run this line of code:

    new Date(new Date().toJSON()); // "Invalid Date"

However, if we use `toString` to serialize dates, then jasmine headless webkit can properly deal with these date objects.

Cons:

* Using `toString` is accurate only to a whole second. `toJSON` will serialize and preserve accuracy down to the millisecond.