NAME:
  rdref
 PURPOSE:   (one line only)
  Read a astrometry support (.ref) file.
 DESCRIPTION:
 CATEGORY:
  File I/O
 CALLING SEQUENCE:
  rdref,file,ref,error
 INPUTS:
  file - Name of file to be read
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  NOFIX - Flag, if set will suppress the attempt to rewrite a file that
            is in the wrong byte order.
 OUTPUTS:
  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 provided 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
  error  - Flag, if set indicates there was a problem reading the file.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
   Files written by astrom.pro (versions prior to 2008/10/31) could have
     been written with the wrong byte ordering.  When a file is read it
     is checked to see if objrad and nstars make sense.  If not, the byte
     order is swapped.  If that extra swap was needed then an attempt is
     made to rewrite the data back to the file thus repairing the file.
     If the file cannot be written to this program will print a warning
     message but will still return good data to the caller.  If the file
     can be written there will be no outward indication that this happened
     other than the file will get changed.
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written 2008/10/31 by Marc W. Buie, Southwest Research Institute.
  2016/04/16, MWB, added error check for non-existent file.