code: def isfortran(env, source):
      
      try:
          fsuffixes = env['FORTRANSUFFIXES']
      except KeyError:
          # If no FORTRANSUFFIXES, no fortran tool, so there is no need to look
          # for fortran sources.
          return 0
  
      if not source:
          # Source might be None for unusual cases like SConf.
          return 0
      for s in source:
          if s.sources:
              ext = os.path.splitext(str(s.sources[0]))[1]
              if ext in fsuffixes:
                  return 1
      return 0
docs: Return 1 if any of code in source has fortran files in it, 0
      otherwise.