Don't require systemd-sysv on newer OSs
    
    Reintroduce a package-level Requires: on systemd-sysv on F19 and
    EL6 and older, where it was a real package that provided the
    systemd-sysv-convert command.  Conditionalized it so it's not required
    on newer releases, and only call systemd-sysv-convert in triggers if we
    have the dependency (#1104138).