[cgiow] (2) Let's allow newlines in <textarea placeholder=''> after all, since there are some valid use cases.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=21286
Affected topics: HTML

git-svn-id: http://svn.whatwg.org/webapps@8204 340c8d12-0b0e-0410-8428-c7bf67bfef74