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:

    validator: focusInvalid() (1, 0, 1)
    29 ms1.Expected at least one assertion, but none were run - call expect(0) to accept zero assertions.