First, add an option in the Site Information config to tell drupal the site can use SSL.

Second, the CAS module will always use SSL when validating a user's ticket.
Third, if a user has any roles other than Anonymous or Authenticated User, they will be given SSL links while "mortal" users will use plain http.

git-svn-id: file:///tmp/wdn_thm_drupal/branches/drupal-7.x@227 20a16fea-79d4-4915-8869-1ea9d5ebf173