Log Message:
graphics/gimp-ufraw: Add default-off gimp option and clean up

  - Add a gimp option, so this can be built with or without the
    gimp(2) plugin.  Default it to off, because gimp3 is nearly here
    and 100% of known users have switched to gimp3.
  - Clean up (c99 moving to USE_CC_FEATURES, sort bl3, prune comments).