Fixed traceback in configuration editor
Fixed traceback in configuration editor

gui/configuration.py:
- QConfigurationTreeWidgetItem.change_value:
  The case where object was a sub-container was not handled correctly.

Ticket: 670

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