[giow] (3) Match reality better in terms of selector case-sensitivity
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=23742
Affected topics: CSS, HTML

git-svn-id: http://svn.whatwg.org/webapps@8253 340c8d12-0b0e-0410-8428-c7bf67bfef74