Add conflicts with older gnome-shell versions
    
    This ensures that we don't end up with new mutter 45.rc and older
    gnome-shell 45.beta, which doesn't work - mutter removed
    meta_rectangle_union() in 45.rc that gnome-shell 45.beta used.
    
    The conflicts here, and gnome-shell having versioned requires on mutter
    make sure that both packages get updated in lock step.
    
    /usr/bin/gnome-shell: symbol lookup error: /usr/lib64/gnome-shell/libshell-13.so: undefined symbol: meta_rectangle_union