Added a new page for manual tests

Find it at localhost:4567/manual. This is for tests which are tricky or impossible to automate.

This new page has just three tests, one to demonstrate that non-remote links don't show the disable-with text when clicked on Safari and Chrome (#306), and two to demonstrate that non-remote links around a div stop working in IE if they have a disable-with attribute (possibly #355).

This new test page uses the same header as the index page to conveniently switch between jquery versions and their source. For that reason the helper methods in server.rb have been updated so they work on other pages than just the index page.