[giow] (3) Another attempt at making directionality in various edge cases more useful and more intuitive.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=17835
Affected topics: HTML, Rendering

git-svn-id: http://svn.whatwg.org/webapps@7955 340c8d12-0b0e-0410-8428-c7bf67bfef74

 Author:    ianh <ianh@340c8d12-0b0e-0410-8428-c7bf67bfef74>