When we decided to no longer show changes to the cookie, we knew that we
would have to change some of the tests. This commit does that for
cookie.t. All the tests that looked at the HTML document now look at the
HTTP response headers.
Changed the tests to no longer assume the default value for
$CookieName. This is important when running the tests on a system
where Apache starts a number of wikis for various virtual hosts and
one of them will end up as the host to use for http://localhost/. That
wiki might very well have a cookie name set.
