NAME: 
  addslash
 PURPOSE: 
  Append a trailing / to string (if needed).
 DESCRIPTION:
 CATEGORY:
  Utility
 CALLING SEQUENCE:
  addslash,name
 INPUTS:
  name - string to modify (scalar or vector)
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  name - string with trailing slash
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  1995/06/08, Written by Marc W. Buie, Lowell Observatory
  1999/02/08, MWB, added clause for Mac style directories.
  2009/02/27, MWB, upgraded to handle vector input.