Move to the new sources file format
    
    This is a pre-requisite to moving away from MD5 sum, as fedpkg will need
    to know which hashtype was used for a give line in the sources file.
    
    Upstream pyrpkg has supported this for long enough now (it was part of
    rpkg-1.32 which is in all Fedora and EPEL branches) that we can make the
    move in fedpkg.
    
    Signed-off-by: Mathieu Bridon <bochecha@daitauha.fr>