[Expo-tech] irritating import of surface GPX stations - now gone away

[Philip Sargent (Gmail)]

It's only 9% of the time importing LoadPos, but it was irritating
watching all those surface legs scroll by none of which would be relevant.

Now fixed using a cache file tied to the timestamp :loser:/1623.svx 
which is used to create the list of x/y/z in 1623.3dtopos. In parsers/survex.py

Philip