[giow] (3) Make sure .click() doesn't fire on disabled form controls.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24404
Affected topics: DOM APIs, HTML

git-svn-id: http://svn.whatwg.org/webapps@8421 340c8d12-0b0e-0410-8428-c7bf67bfef74