Some preliminary work at making use of this driver led me to implement
CRC-16 checks on read and write to deal with the occasional glitchiness of
the 1-Wire bus. The revised driver (attached) returns an I/O error if the
CRC check fails. When reading the chip's state, either you get a valid
indication or you get an I/O error. When changing its state, either the
change is successful or an I/O error is returned.