The previous name was confusing as another mechanism for debugging also
use the term 'dump' for something not related to interpolator reuse.

Fixes issue #189

Fixes issue #189

This is an attempt at solving issue #188.

This algorithm is similar in spirit to the IGNORE_DEM_USE_ELLIPSOID, but
with a user-specified elevation instead of always using 0.0 elevation.

Implements feature #187.

Thanks to Espen Bjørntvedt for the translations.

The derivatives are computed with respect to transforms parameters.
This is the first step towards los calibration.