Fix bug in definition of upstream and downstream nodes
Fix bug in definition of upstream and downstream nodes

berkeley-cocosci/Wallace,Dallinger/Dallinger,jcpeterson/Dallinger,jcpeterson/Dallinger,jcpeterson/Dallinger,Dallinger/Dallinger,Dallinger/Dallinger,Dallinger/Dallinger,Dallinger/Dallinger,berkeley-cocosci/Wallace,jcpeterson/Dallinger,suchow/Wallace,suchow/Wallace,jcpeterson/Dallinger,suchow/Wallace,berkeley-cocosci/Wallace