dem_mosaic: First cut

dem_mosaic: First cut
dem_mosaic: More work
dem_mosaic: Do grassfire in tile plus bias only, also erode
dem_mosaic: Condense code
stereo.cc: More error checking
dem_mosaic: More simplification
dem_mosaic: Use projected space rather than lonlat space
Condense repeated code
Clarify docs a bit
Minor clarifications
dem_mosaic: Handle reprojection
dem_mosaic: Robustness, first cut at doc
mapproject and Common: Minor wording and comments
dem_mosaic: Handle reprojection better
dem_mosaic: doc and news