Improves how to initialize polymer apps and fixes polymer build and linter to

pkg/polymer/lib/builder.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Common logic to make it easy to run the polymer linter and deploy tool.
  *
  * The functions in this library are designed to make it easier to create
  * `build.dart` files. A `build.dart` file is a Dart script that can be invoked
  * from the command line, but that can also invoked automatically by the Dart
@@ skipping 261 matching lines @@
         help: 'Remove any build artifacts (if any).')
     ..addFlag('full', negatable: false, help: 'perform a full build')
     ..addFlag('machine', negatable: false,
         help: 'Produce warnings in a machine parseable format.')
     ..addFlag('deploy', negatable: false,
         help: 'Whether to force deploying.')
     ..addOption('out', abbr: 'o', help: 'Directory to generate files into.',
         defaultsTo: 'out')
     ..addFlag('help', abbr: 'h',
         negatable: false, help: 'Displays this help and exit.');
-  var res = parser.parse(args == null ? new Options().arguments : args);
-  if (res['help']) {
-    print('A build script that invokes the polymer linter and deploy tools.');
+
+  showUsage() {
     print('Usage: dart build.dart [options]');
     print('\nThese are valid options expected by build.dart:');
     print(parser.getUsage());
+  }
+
+  var res;
+  try {
+    res = parser.parse(args == null ? new Options().arguments : args);
+  } on FormatException catch (e) {
+    print(e.message);
+    showUsage();
+    exit(1);
+  }
+  if (res['help']) {
+    print('A build script that invokes the polymer linter and deploy tools.');
+    showUsage();
     exit(0);
   }
   return new CommandLineOptions(res['changed'], res['removed'], res['clean'],
       res['full'], res['machine'], res['deploy'], res['out']);
 }