Specify required gtk2 and gtk3 versions
    
    gnome-themes-standard 3.6.5 requires a newer gtk2 version than is in the
    base F18 repo. This adds the minimum required versions to the deps, to
    ensure that the correct gtk versions from updates are installed.
    
    (cherry picked from commit ec5a8b5d3027ac4c35f9723438cb924e532db98a)