Make stereo handle holes in DEM

tmp3
MapTransform: comments added
renamed:    MapTransform.cc -> GroundToCameraTransform.cc
renamed class MapTransform to GroundToCameraTransform
MapTransform: Wipe old class, and rename
renamed:    GroundToCameraTransform.cc -> Map2CamTrans.cc
Map2CamTrans: Indent