Add Obsoletes to better handle upgrade path from before -libs was introduced
    
    Could theoretically replace the 2 obsoletes with a single
    Conflicts: gdbm < 1:1.14.1-4
    in -libs, but I think Obsoletes approach more closely follows
    https://fedoraproject.org/wiki/Upgrade_paths_%E2%80%94_renaming_or_splitting_packages
    in spirit