Update cgi-style to match the new web site look.
Add an optional 2nd argument to html_header(); if it's missing or
supplied and non-zero, html_header returns XHTML doctype; if it's
supplied and zero, html_header returns HTML 4.01 doctype.
cvsweb and mailindex are the only HTML4 holdouts. cvsweb should
be updated to 3.x which is XHTML, but that's a seperate step.
I left $hsty_home alone, because I couldn't find anything that used
it or any obvious image to use for it in the new layout.