[aci] (0) With great reluctance, admit X-UA-Compatible exists.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=27091
Affected topics: HTML, HTML Syntax and Parsing

git-svn-id: https://svn.whatwg.org/webapps@8870 340c8d12-0b0e-0410-8428-c7bf67bfef74
Merge remote-tracking branch 'origin/master' into whatwg