User link hovering does not work in the recent changes macro

When hovering on a user link, only the drop shadow of the hover menu appears.

How to reproduce: Visit http://confluence.atlassian.com/pages/recentlyupdated.action?key=DOC and hover over a username in the recently updated menu.

Reason: The hovering script can't find the username and therefore tries to look up the user "undefined". This happens as the username is supplied as a CSS class in the link and not in the "data-username" attribute as expected by the hovering script. A fixed version of the UserLink class is attached.