NAME:
  refgen
 PURPOSE:   (one line only)
  Generate a source/catalog cross-reference list
 DESCRIPTION:
 CATEGORY:
  Astrometry
 CALLING SEQUENCE:
  refgen,astinfo,fnsrc,catfile,ref
 INPUTS:
  astinfo - Anonymous structure that contains an astrometric description
               of a image-based coordinate system and its mapping to the
               celestial sphere.  (see mkastinfo for more information)
  fnsrc   - Name of source file to read (generated by findsrc.pro)
  catfile - Name of catalog sub-file to read (generated by refnet.pro)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  ref     - Anonymous structure with the cross-linked list (see rdref/wrref)
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  Written by Marc W. Buie, Southwest Research Institute, 2010/01/14
  2010/07/26, MWB, minor mod for new frmdxdy error codes