Fixed usage message

main.ml

@@ -53,7 +53,7 @@ let parse_args () =
              "   Optional input file (default is to read from stdin)");
 
     ("-o", Arg.String (fun s -> Globals.args.outfile <- Some s),
-         "<file> Output file (defaults to foo.s for foo.cvc)");
+         "<file> Output file (defaults to stdout)");
 
     ("-v", Arg.Int (fun i -> Globals.args.verbose <- i),
          "<num>  Set verbosity (0: nothing, 1: errors, 2: intermediate, 3: debug)");