TODO

gdal_contrast_stretch:
    * allow 16-bit output
    * several inputs for contrast stretch
    * manual min/max for contrast stretch
      (gdal_translate -scale already does this)

gdal_trace_outline:
    * for feature classification, trace all feature classes simultaneously (for
      much better speed)
    * run erosion several times for outline tracer
    * expose options for fuzzy rectangle bounds finder
    * use concave hull instead of the current excursions pincher
    * outline tracer should call OGR_G_IsValid on result

gdal_list_corners: fails on venus gtdr.tif (lat>90)
dem2rgb: prominant warning if resolution not known
dem2rgb: should be operable with resolution in absence of origin
gdal_merge_simple: usage text wrong?
don't use %f, use %g with the right number of digits