Pending class

This pull request adds a "pending" class to the input element while there is remote validation pending. This allows you, for example, to add a loading animation to visually indicate that there outstanding activity for the field.

The new unit test passes in IE, safari, chrome and firefox. There is a unit test failing in IE, but it is not one I wrote, and it was already failing in my version of IE before I added my code:

    validator: focusInvalid() (1, 0, 1)
    29 ms1.Expected at least one assertion, but none were run - call expect(0) to accept zero assertions.

No sure if i need this submit handler, since it's already tested by an earlier test. 
I find it a little confusing that we're testing the submit handler in addition to the pending class.
If you agree I can remove it and submit a separate pull request.