New file with function python_module_exists() and exception MissingRequirement().
New file with function python_module_exists() and exception MissingRequirement().

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