Fixes Issue #382

Fixed issues #379 and #378

This should fix a minor vulnerability CVE-2019-9658, related to default
loading of external entities.

Direct location is performed in two phases, with a first intersection
being computed without corrections, then correction are applied and the
first solution is "refined". It was expected that the DEM cell did not
change there. Unfortunately, sometimes the refining did not find a
result in the same DEM cell. This was a very rare occurrence, and was
detected first on very ... rugged areas like mountains.

Now, when this rare event is detected, we restart a full-blown
intersection but starting from a point just after the exit of the
failing cell, when LOS is still above DEM and we prevent the algorithm
to find solutions backward (i.e. we prevent it from finding the previous
solution again and looping infinitely).

In the updateTile method (to be developed by the user according to the
kind of raster to be read), it happens that some useless data are
dumped. For instance, when reading some SRTM data, one needs to read
also some Geoid data. When reading the Geoid data, the elevations may be
dumped (if using the SimpleTile.interpolateElevation method).