preferences.py: Switched test from dialogs to URL
preferences.py: Switched test from dialogs to URL

VisTrails/VisTrails,hjanime/VisTrails,minesense/VisTrails,hjanime/VisTrails,minesense/VisTrails,hjanime/VisTrails,minesense/VisTrails,minesense/VisTrails,hjanime/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails,minesense/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails