NAME:
  sortcube
 PURPOSE:   (one line only)
  Sort an image cube by brightness at each pixel
 DESCRIPTION:
 CATEGORY:
  CCD data processing
 CALLING SEQUENCE:
  sortcube,incube,outcube
 INPUTS:
  incube - 3-D image cube to be sorted
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  outcube - 3-D image cube with the brightest pixels in plane 0, faintest
               pixels in the last plane.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2012/07/16, Written by Marc W. Buie, Southwest Research Institute based on
                 and algorithmic description provided by Mark Showalter.