www_coderepo: tree: do not break #n$LINENO

www_coderepo: tree: do not break #n$LINENO

We can't use 302 redirects at the /tree/ endpoint as originally
intended since "#n$LINENO" fragment links aren't preserved
across redirects (since clients don't typically send that part
of the URL in requests).

So we'll have to make sure we handle prefixes properly and show
trees directly.  Oh well :<  At least the history-aware 404
handling remains :>