cgi: /$LISTNAME/ and /$LISTNAME/index.html are equal
This prevents ambiguity when switching URLs between static
file servers and CGI.
The /$LISTNAME/index.html URL appearing in the wild is inevitable
because of our static file server support. Worst yet, there's
no easy/consistent way to get all installations detect and 301
them to the shorter /$LISTNAME/. So we make the CGI support
/$LISTNAME/index.html.
The downside of this is the potential duplicate entry in all caches.