NAME:
  wrref
 PURPOSE:   (one line only)
  Write a astrometry support (.ref) file.
 DESCRIPTION:
 CATEGORY:
  File I/O
 CALLING SEQUENCE:
  wrref,file,ref,error
 INPUTS:
  file - Name of file to be written
  ref  - Anonymous structure that contains the information read from file.
            Tags in structure always provided:
              objrad - object aperture radius (pixels)
              nstars - Number of stars in the list
            Tags needed if nstars > 0
              xpos    - float, X position of star
              ypos    - float, Y position of star
              fwhm    - float, FWHM of object (pixels)
              mag     - float, instrumental magnitude of star
              err     - float, uncertainty on magnitude
              sig_max - float, DN value of peak pixel in image
              ra      - double, RA of star (radians)
              dec     - double, Dec of star (radians)
              catmag  - float, Catalog magnitude for star
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  error  - Flag, if set indicates there was a problem writing the file.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written 2008/10/31 by Marc W. Buie, Southwest Research Institute.
  2009/07/29, MWB, explicit cast of data to make sure file contains the
                correct type of data.