code: def _makeJobSuccessorReadyToRun(self, jobGraph, jobNode):
          
          successorJobStoreID = jobNode.jobStoreID
          #Build map from successor to predecessors.
          if successorJobStoreID not in self.toilState.successorJobStoreIDToPredecessorJobs:
              self.toilState.successorJobStoreIDToPredecessorJobs[successorJobStoreID] = []
          self.toilState.successorJobStoreIDToPredecessorJobs[successorJobStoreID].append(jobGraph)
  
          if jobNode.predecessorNumber > 1:
              return self._checkSuccessorReadyToRunMultiplePredecessors(jobGraph, jobNode, successorJobStoreID)
          else:
              return True
docs: make a successor job ready to run, returning False if they should
          not yet be run