NAME:
  rdreduc
 PURPOSE: 
  Reader for a reductor info file (reduc.inf)
 DESCRIPTION:
  Reads all fields of the reduc.inf file, including the rules. If the
  info file is not the latest version, it is promoted with reducprmt.
 CATEGORY:
  Photometry
 CALLING SEQUENCE:
  rdreduc,infofile,inst,ddir,rundate,rad,sky1,sky2,gain,rdnoise,oplines
 INPUTS:
  infofile-   filename for the info file.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  GUI-     Flag, if set use widgets to prompt for any additional inputs.
              This flag is also passed to reducprmt.
  RDNOISE- default read noise, passed to reducprmt.
 OUTPUTS:
  inst  -  name of instrument for the run. Will be a NULL string
              if the info file cannot be found.
  ddir  -  path to image data for the run.
  rundate- date code for the run, six digit string.
  rad-     float, object aperture radius in pixels.
  sky1-    float, inner sky annulus radius in pixels.
  sky2-    float, outer sky annulus radius in pixels.
  gain-    float, instrument gain in e-/DN
  rdnoise- float, instrument read noise in e-/pixel.
  oplines- string array, rule lines ( line 6 and beyond of info file)
             Will be a single null string if there are no rule lines
             or the infofile cannot be found.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
  Will rewrite infofile if it is promoted.
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  2006/08/25   Written, Peter L. Collins, Lowell Observatory
  2009/12/31, MWB, minor tweak to protect against output variables having
                 values (and rank) upon input.