fix links with children in overlay

This replaces `e.target` by `this` in the code from #802. According to http://api.jquery.com/on/ `e.target` is the innermost element the event originates from. `this` is not (as I had previously though) the element `on()` is called on but the one in the second argument to `on()`. So this fixes cases were links have child elements (e.g. images).