Show better error messages in network failures.

utils/pub/io.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.
 
 /**
  * Helper functionality to make working with IO easier.
  */
 library io;
 
 import 'dart:io';
@@ skipping 694 matching lines @@
 }
 
 /**
  * Exception thrown when an HTTP operation fails.
  */
 class PubHttpException implements Exception {
   final int statusCode;
   final String reason;
 
   const PubHttpException(this.statusCode, this.reason);
+
+  String toString() => 'HTTP error $statusCode: $reason';
 }
 
 /**
  * Exception thrown when an operation times out.
  */
 class TimeoutException implements Exception {
   final String message;
 
   const TimeoutException(this.message);
+
+  String toString() => message;
 }
 
 /**
  * Contains the results of invoking a [Process] and waiting for it to complete.
  */
 class PubProcessResult {
   final List<String> stdout;
   final List<String> stderr;
   final int exitCode;
 
@@ skipping 23 matching lines @@
   return new Directory(entry);
 }
 
 /**
  * Gets a [Uri] for [uri], which can either already be one, or be a [String].
  */
 Uri _getUri(uri) {
   if (uri is Uri) return uri;
   return new Uri.fromString(uri);
 }