Improve scrub_future_sys_modules()
Improve scrub_future_sys_modules()

- Based on commit e57ca2f89: "More fixes and improvements to the sys.modules cleaning"

michaelpacer/python-future,PythonCharmers/python-future,QuLogic/python-future,michaelpacer/python-future,QuLogic/python-future,PythonCharmers/python-future,krischer/python-future,krischer/python-future