When we get a request for http:foo.com/bar,
bar is a directory and contains an index.html,
we need to send back a redirect for http:foo.combar
(i.e. add the final slash),
otherwise relative links from index.html will be relative to http:foo.com/
instead of http:foo.combar.
E.g. look at http:www.haskell.orghappy.