NAME:
  etut
 PURPOSE:   (one line only)
  Compute ET-UT time offset for a given Julian Date
 DESCRIPTION:
 CATEGORY:
  Astronomy
 CALLING SEQUENCE:
   ans = etut(jd)
 INPUTS:
   jd - Julian Date (UTC), scalar or vector
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
   Return value which is the difference of ET-UT for the given JD.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
   Needs to have access to the file, leapsec.dat.  This file is periodically
     updated as new leap-seconds are announced.  This file is contained as
     part of this library.
 PROCEDURE:
 MODIFICATION HISTORY:
  2010/12/02, Written by Marc W. Buie based on a routine provided by
                Larry Wasserman which was in turn adapted from a routine
                supplied to him by Myles Standish.