Assertion ElementHasAttributes added.

Proposing, `browser.assert.elementHasAttributes( [docString,] selector, attributesHash)`
That asserts that the element contains `attribute:value` pairs specified by attributesHash.

Drop the `assert.truthy` above and instead prepend this test before this line:

```coffeescript
        assert.hasType 'elementHasAttributes(selector, attributesObject) - requires textOrRegExp value', RegExp, val
```

This way, you again get to see what the actual type and value was, when a bad value was passed.