Fixing some user feedback
    
    For each source without upstream, f-r outputs a message about the
    missing upstream, and this being "a corner case not yet supported".
    This is plain wrong, f-r will will never be able to create upstreams
    for sources missing it.
    
    Removing this output completely. There's already another message "No
    upstream for whatever" displayed which gives the correct user feedback.
    
    Fixing messages while downloading, correctly state when cache is used.