Comment 12 for bug 1549156

The logic responsible for this is http://bazaar.launchpad.net/~unity-team/unity8/trunk/view/head:/qml/Dash/Previews/PreviewSharing.qml#L60

Every uri that doesn't start with file:// or "/" is considered external. And there is a comment in the code saying " for now, treat all external urls as Links, or it will break contenthub"