Really test that the jump to mapping dialog finds a site

- Before, this was only testing for the presence of the site host in
  any form, which would have matched on the error page's <p> tag and
  passed. We don't want it to match an error page, we want to know that
  the site has been found, so test for the site URL in header text.
- Add a test for the "Unknown site" error page case.