Check all upgrade nodes for thumbnails when comparing
Check all upgrade nodes for thumbnails when comparing

    core/vistrail/controller.py:
    - execute_workflow_list:
      Check all previous upgrade nodes for thumbnails to compare with

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