Fix a bug encountered when updating PythonSource or MplPlot.  Check if aliases[i] exists.
Fix a bug encountered when updating PythonSource or MplPlot.  Check if
aliases[i] exists.

core/vistrail/controller.py:
  - VistrailController.update_function_ops: check if aliases[i] exists
    before setting it



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