Fix mis-use of span within fieldset.

Fix mis-use of span within fieldset.

div and span is inter-changable as they can be styled via css, But we should
really use div element within fieldset instead of span element by default. I
believe using div here is the sane default. ;-)

below urls are for references:
http://www.learnwebdesignonline.com/htmlcourse/span-div.htm
http://archive.thedevweb.com/2007/0502.html