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

bin/format.dart

Index: bin/format.dart
diff --git a/bin/format.dart b/bin/format.dart
index a8375eb671b4f086a0658063c9cfe2660cf28d06..3c56b134ebc9cd7b80e63faba73f2b937f0fea95 100644
--- a/bin/format.dart
+++ b/bin/format.dart
@@ -19,6 +19,8 @@ void main(List<String> args) {
   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 {
@@ -101,7 +103,7 @@ void printUsage(ArgParser parser, [String error]) {
 
   output.write("""$message
 
-Usage: dartformat [-l <line length>] <files or directories...>
+Usage: dartformat [-w] <files or directories...>
 
 ${parser.usage}
 """);