- bugfix get_release(): if ${MapDirsToOverlays[${dir}]} is empty this
  does not imply that the module is not somewhere in out hierarchy
- improved  find_overlay(): Use ${MapDirsToOverlays[${dir}]}:
  if it is set we don't have to loop over all overlays
  if it not set lookup overlay for dir and add to the map
- review subcommand_load():
  - output_load_hints() renamed to get_load_hints(), return hints in an
    upvar
  - on conflicts output module(s) the to be loaded module conflicts
    with