reverseTopologicalOrder :: GenericInstallPlan ipkg srcpkg iresult ifailure
                        -> [GenericPlanPackage ipkg srcpkg iresult ifailure]
reverseTopologicalOrder plan =
    map (planPkgOf plan)
  . Graph.topSort
  $ planGraphRev plan
reverseTopologicalOrder :: GenericInstallPlan ipkg srcpkg iresult ifailure
                        -> [GenericPlanPackage ipkg srcpkg iresult ifailure]
reverseTopologicalOrder plan =
    map (planPkgOf plan)
  . Graph.topSort
  $ planGraphRev plan
reverseTopologicalOrder plan =
    map (planPkgOf plan)
  . Graph.topSort
  $ planGraphRev plan