remote-mediawiki: show known namespace choices on failure
If we fail to find a requested namespace, we should tell the user
which ones we know about, since those were already fetched. This
allows users to fetch all namespaces by specifying a dummy namespace,
failing, then copying the list of namespaces in the config.
Eventually, we should have a flag that allows fetching all namespaces
automatically.
Reviewed-by: Antoine Beaupré <anarcat@debian.org>
Signed-off-by: Antoine Beaupré <anarcat@debian.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>