compose: fix --download-only for force and make it work right
    
    Whoops, this is embarrassing. `compose --download-only` was
    broken two different ways: `--force` didn't work right (because
    of the annoying way mediawiki handles it, which I forgot about)
    and more importantly, relval didn't quit after creating the
    download page, it'd just carry right on into the 'create the
    entire compose' stuff :(