Allow "-t" flag to preserve compability with old formatter. Fix #166.

bin/format.dart

 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:dart_style/src/io.dart';
 
 void main(List<String> args) {
   var parser = new ArgParser(allowTrailingOptions: true);
 
   parser.addFlag("help", abbr: "h", negatable: false,
       help: "Shows usage information.");
   parser.addOption("line-length", abbr: "l",
       help: "Wrap lines longer than this.",
       defaultsTo: "80");
   parser.addFlag("dry-run", abbr: "n", negatable: false,
       help: "Show which files would be modified but make no changes.");
   parser.addFlag("overwrite", abbr: "w", negatable: false,
       help: "Overwrite input files with formatted output.\n"
             "If unset, prints results to standard output.");
   parser.addFlag("follow-links", negatable: false,
       help: "Follow links to files and directories.\n"
             "If unset, links will be ignored.");
+  parser.addFlag("transform", abbr: "t", negatable: false,
+      help: "Unused flag for compability with the old formatter.");
 
   var options;
   try {
     options = parser.parse(args);
   } on FormatException catch (err) {
     printUsage(parser, err.message);
     exitCode = 64;
     return;
   }
 
@@ skipping 62 matching lines @@
   var output = stdout;
 
   var message = "Reformats whitespace in Dart source files.";
   if (error != null) {
     message = error;
     output = stdout;
   }
 
   output.write("""$message
 
-Usage: dartformat [-l <line length>] <files or directories...>
+Usage: dartformat [-w] <files or directories...>
 
 ${parser.usage}
 """);
 }