Simpler implementation of depends_on.
Simpler implementation of depends_on.

krafczyk/spack,mfherbst/spack,LLNL/spack,tmerrick1/spack,matthiasdiener/spack,tmerrick1/spack,krafczyk/spack,TheTimmy/spack,EmreAtes/spack,EmreAtes/spack,iulian787/spack,lgarren/spack,tmerrick1/spack,iulian787/spack,TheTimmy/spack,TheTimmy/spack,lgarren/spack,lgarren/spack,krafczyk/spack,matthiasdiener/spack,matthiasdiener/spack,TheTimmy/spack,tmerrick1/spack,lgarren/spack,iulian787/spack,skosukhin/spack,krafczyk/spack,krafczyk/spack,matthiasdiener/spack,mfherbst/spack,skosukhin/spack,tmerrick1/spack,matthiasdiener/spack,LLNL/spack,lgarren/spack,skosukhin/spack,LLNL/spack,LLNL/spack,skosukhin/spack,iulian787/spack,skosukhin/spack,EmreAtes/spack,EmreAtes/spack,EmreAtes/spack,mfherbst/spack,mfherbst/spack,TheTimmy/spack,iulian787/spack,LLNL/spack,mfherbst/spack