Removes circular dependency system<->requirements
Removes circular dependency system<->requirements

core.system imported core.requirements which wasn't safe.

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