Add script to find differences between package versions.
Add script to find differences between package versions.

scripts/diff_package.py:
  - new script

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