added test to make sure area is unmapped
added test to make sure area is unmapped

Linux-Comedi/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,olsonse/comedilib,olsonse/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,Linux-Comedi/comedilib,Linux-Comedi/comedilib,olsonse/comedilib,olsonse/comedilib,Linux-Comedi/comedilib