<bugfix>Vistrail Variable list was changing while being iterated over</bugfix>
<bugfix>Vistrail Variable list was changing while being iterated over</bugfix>

gui/variable_dropbox.py:
- QVariableDropbox.updateController:
  Iterate over a copy of vistrail_vars to avoid it changing

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