Temperature Readings of 85C are being transmitted

[crouchingbadger]

When the temperature sensor fails to read a temperature it returns 85. This is being accepted as a valid reading rather than being rejected. As a result the temperature compensation code causes Distance readings to fluctuate.

Consider

1. debugging and looking for the cause of a failed read.
2. writing validation code where readings of 85 degrees need to either be rejected or transmit an error.
3. Modifying Nominet bridge code to reject or annotate errors.