FedoraMessaging plugin fixes - correct headers
    
    So, AMQP wire format is a bit wacky and leads to very confusing
    conversations, because there's a header frame with a field called
    'headers', and there's headers you put in the header frame and
    headers you put in the 'headers' field in the header frame, and
    they're not the same thing! Sigh. Software...also, add some
    headers (of both kinds!) that we're supposed to have, but didn't
    before, and update the package description.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>