nib2gmodel will not build on OpenStep 4.2

[Pete French]

problem: make/create_domain_dir_tree.sh uses dirname which does not
         exist under OpenStep 4.2

solution: as it is merely used to find the directory being run in then 
          it can be replaced with something like:


        mybase=`basename $0`
        mydir=`echo $0 | sed -e "s/\/${mybase}//"`


-bat.