[giow] (3) Make <fieldset> display:block to match implementations
Fixing https://www.w3.org/Bugs/Public/show_bug.cgi?id=27018
Affected topics: HTML Syntax and Parsing, Rendering

git-svn-id: https://svn.whatwg.org/webapps@8842 340c8d12-0b0e-0410-8428-c7bf67bfef74