Support for dates in assertEquals and assertEqualsEpsilon

This allows tests like the following:

```javascript
function testAssertEquals() {
    var reunion = new Date(1990, 10, 3),
        nextDay = new Date(1990, 10, 4);

    this.epsilon = 24 * 60 * 60 * 1000; // h * min * sec * ms
    this.assertEqualsEpsilon(reunion, nextDay);
}
```