[giow] (1) Set the .relatedTarget attribute on 'click' events for <menuitem> elements (and their master commands) properly.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=17840
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@7792 340c8d12-0b0e-0410-8428-c7bf67bfef74