Added default constructor for comedi::subdevice, and added missing wrapper for comedi_cancel().
Added default constructor for comedi::subdevice, and added missing wrapper
for comedi_cancel().

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