[giow] (2) Make RadioNodeList's radio button logic support the magical 'on' value.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=26353
Affected topics: DOM APIs

git-svn-id: http://svn.whatwg.org/webapps@8744 340c8d12-0b0e-0410-8428-c7bf67bfef74