The po plugin needs to be updated to match the urlto sub API and
signature changes. Else a wiki with the po plugin enabled cannot be
refreshed / rebuilt because of (correct) Perl errors.

My po branch contains a fix.

Also, I fear the lack of any useful `$from` parameter might break some
l10n'd link niceness when using `po_link_to = current` but I have not
investigated this yet.

--[[intrigeri]]