anchor.diff:  
   let bc_start = "(*--build-config"
   let bc_end   = "--*)"
  -let open_file (filename:string) =
  +
  +let find_file (filename:string) : string =
  +  if System.IO.Path.IsPathRooted filename then filename
  +  else
       let include_path = Options.get_include_path() in
       try
           let p = Util.find_map include_path (fun p ->
  
positive.code:                 then Some path
                  else None) in
          match p with
          | Some f ->
              if !Options.debug <> []
              then Util.fprint1 "Opening file: %s\n" f;
              new System.IO.StreamReader(f)
          | _ -> raise (Absyn.Syntax.Err("unable to open file"))
      with e -> raise (Absyn.Syntax.Err (Util.format2 "Unable to open file: %s\n%s\n" filename (e.ToString())))
  
  
  let read_build_config (filename:string) =
      let fail msg = raise (Absyn.Syntax.Err(Util.format2 "Could not parse a valid build configuration from %s; %s" filename msg)) in
  
negative.code:               files
      else if !Options.use_build_config //the user claimed that the build config exists
      then fail ""
      else (Options.admit_fsi := "FStar.Set"::!Options.admit_fsi;
            ["set.fsi"; "heap.fst"; "st.fst"; "all.fst"; filename])
  
  let parse fn =
    Parser.Util.warningHandler := (function
  