Fix CRS file granularity

Using the CompuTrainer utility to convert GPS logs to a course profile
results in lots of very small segments where the height differences are
less than 1 metre. These were incorrectly handled as the altitude was
being stored as a long.

In fact the double to long conversion was always rounding down, for
instance 200+0.01 is 200 as expected, but 200-0.01 is 199. Therefore the
course would gradually ratchet downhill with every small data point.