How can you detect if the client browser has SSL support? I am not refering
about the server Variables HTTPS_* . Those variables are only set when the
user enters the site using HTTPS://site_name. I want to be able to determine
if the browser has not SSL support, so I can redirect the user to a a unsecured
page explaining the problem.

P.S. I know this is possible because this company (http://www.cyscape.com)
has a product that can even detect when you unselect SSL support from your
browser options.