[giow] (3) Handle the case of removing the 'src' attribute on a live <iframe>, and some minor clarity changes.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=23637
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@8289 340c8d12-0b0e-0410-8428-c7bf67bfef74