<bugfix>Fix broken clipboard check for paste</bugfix> <ticket>#680</ticket>
<bugfix>Fix broken clipboard check for paste</bugfix>
<ticket>#680</ticket>

not QString.isEmpty != not str

vistrails/gui/pipeline_view.py:
  - QPipelineView.clipboard_non_empty: fix logic

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