click handler returns false

If you have a link with `remote: true`, currently confirming it with twitter-bootstrap-rails-confirm causes a "#" to be added to the location. This is because the ".proceed" click handler returns true, allowing the default "a" click handler to fire, so the href "#" gets visited. Nothing breaks if we return false, however, because that's what the `callback()` method is for.

I've tested this on one of my apps, and it appears to work fine for both `remote: true` and `remote: false`.