NAME:
  relpath
 PURPOSE: 
  Prepend a path to the file name if file starts with {\tt +}
 DESCRIPTION:
 CATEGORY:
  Utility
 CALLING SEQUENCE:
  repath,filename,path
 INPUTS:
  filename - Name of file
  path     - Name of directory
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
 OUTPUTS:
  filename - path is prepended if filename starts with +, otherwise filename
             is left unchanged.
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  95/08/07 - Written by Marc W. Buie, Lowell Observatory