Android Pilot Altimeter & VSI v1.2c

I released version 1.2c a couple of days ago.

With the help of Andrew Dobie Tanpaw for which I'm very grateful indeed, I eventually found that the timestamp returned by SensorEvent differs between various Android versions.

It seems to be the case that on earlier Android versions, the timestamp refers to nanoseconds since the time the device was booted; in later Android versions, the timestamp refers to nanoseconds since the epoch (start of 1970).

I determined empirically that the timestamp on my Nexus 4 refers to nanoseconds since 1970 and produced a compatible timestamp when the altimeter was being drawn, which was used for the purposes of filtering. Unfortunately this did not work on some devices because the timestamp did not have the same point of reference, and it caused the program on those models to crash.

Since it is never officially documented what the timestamp refers to, I have taken the decision to leave out filtering when the altimeter is drawn; filtering now occurs only when samples come in.

I have also added the capability since the last release of moving the program to SD card where appropriate.