[giow] (0) Focus the dialog for dialog.show() as well.
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=24718
Affected topics: CSS, DOM APIs, HTML

git-svn-id: http://svn.whatwg.org/webapps@8487 340c8d12-0b0e-0410-8428-c7bf67bfef74