<bugfix>enabling/disabling package did not invalidate pipeline</bugfix>
<bugfix>enabling/disabling package did not invalidate pipeline</bugfix>

This issue was introduced by ticket 584

gui/preferences.py:
- QPackagesWidget.enable_current_package, disable_current_package:
Re-added invalidate_current package call

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