Fix issue with optional ports.  Also fix Mac connection drawing bug.
Fix issue with optional ports.  Also fix Mac connection drawing bug.

gui/pipeline_view.py:
  - QGraphicsConnectionItem.create_path: perturb the second control
    point to try to get rid of an issue with Mac OS X
  - QGraphicsModuleItem.getPortPosition: fix bug with what should be
    returned and make sure registry is available

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