Fix deleting characters not triggering validation in IE9.

This fixes validation failing after deleting text in IE9.

See the IE9 note under Browser Compatibility [here](https://developer.mozilla.org/en-US/docs/Web/Events/input).

The code disables the keyup event handler if the input event is available. Even though the input event is available in IE9, it doesn't fire on deletions. The fix is to not register the input event handler in IE9, falling back to the keyup checks.

Check for IE9 version came from here: http://tanalin.com/en/articles/ie-version-js/