Restore the old message format.
    
    The message format broke in 3cb41aa5dc2e11ff698cb2c3775ae96534d02dff
    
    The resulted in tracebacks in pdc-updater when it tried to learn things
    about a module that was just submitted.  It relied on certain fields
    (`stream`) being in the message body.  This change restores those fields
    to get things working again.