[ bug originally reported by Simon Paillard ]

/latest redirection currently works only for the webapp, but not for the static
data served directly by the web server, and most notably stuff under /data . We
should be uniform and implement /latest redirection for /data

To implement that, we could either generate static redirection maps for Apache
at each update run. Or decide that /data stuff can be served by the webapp
(assessing the corresponding performance penalty) and reuse the code we already
have in place for the redirection.