[Therion] Strange Therion/survex disparity in altitudes

[Andrew Atkinson]

> DOWN has been mis-converted into +90 rather than -90, when converting
> from Survex format to Therion format.
> Survex:
> 2213	2212	B	3.49	-	DOWN
> Therion:
> 2213  2212    3.49  311  90
> I'm guessing that error may turn up elsewhere. consort_climax looks
> similarly wrong.
As a point to note -90 and Down at treated differently for clino 
correction, they can be treated ed the same

 From the survex manual

     "*infer plumbs on" tells cavern to interpret gradients of +/- 90 
degrees as UP/DOWN (so it will not apply the clino correction to them). 
This is useful when the data has not been converted to have UP and DOWN

Andrew