[ct] (2) Make the outline algorithm handle sectioning roots more sensibly
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24100
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@8358 340c8d12-0b0e-0410-8428-c7bf67bfef74