[c] (0) Disallow <dialog tabindex>, for sanity
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24714
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@8488 340c8d12-0b0e-0410-8428-c7bf67bfef74