Only preventDefault on click on [data-toggle="modal"] when the element is a link

In it's current state Bootstrap always prevents the default action for a click event on `[data-toggle="modal"]` elements (see https://github.com/twbs/bootstrap/blob/master/js/modal.js#L233). Instead this should only happen when the element is a link.

Why? I'm opening a modal when the user chooses a particular radio button. But with the current Bootstrap version the radio button won't get selected, but the modal opens. I think the only reason why `preventDefault` is needed is to prevent the hash from appearing in the URL (and thus the browser from jumping to the top or said hash).