Add dependency-finding script
    
    This script lists all dependencies of a set of packages (as given on the
    command line) which are maintained by the SIG. This includes recursive
    dependencies.
    
    To show the help text:
    
        ./scripts/intersection.sh --help
    
    To show SIG packages which are required by Dogtag PKI:
    
        ./scripts/intersection.sh pki-ca
    
    Signed-off-by: Alexander Scheel <ascheel@redhat.com>