Hide Modal when background is clicked

The handleBackdropClick handler should also bind to div.modal . Otherwise, clicking the background does nothing. The .modal is fullscreen as in the http://getbootstrap.com/javascript/#modals examples and catches the click before it arrives to the .modal-backdrop.

This restores the functionality broken in https://github.com/stevoland/react-bootstrap/pull/66

I guess the ordering of the .modal-backdrop and .modal can based on the markup so it's best to handle both cases.