Further fixes for Ticket #180
Further fixes for Ticket #180

core/vistrail/vistrail.py:
  - Vistrail.pruneVersion: do a dfs on the version graph to delete child tags
      of a pruned version



minesense/VisTrails,VisTrails/VisTrails,Nikea/VisTrails,celiafish/VisTrails,hjanime/VisTrails,minesense/VisTrails,hjanime/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,minesense/VisTrails,minesense/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails,minesense/VisTrails,celiafish/VisTrails,Nikea/VisTrails,hjanime/VisTrails,Nikea/VisTrails,celiafish/VisTrails,Nikea/VisTrails,VisTrails/VisTrails,hjanime/VisTrails,celiafish/VisTrails