[giow] (0) Update how 'br' is specced at the CSS level. This depends on as-yet incomplete CSS changes.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=25503
Affected topics: Rendering

git-svn-id: http://svn.whatwg.org/webapps@8745 340c8d12-0b0e-0410-8428-c7bf67bfef74