Better error-message when bind fails.

tests/standalone/io/socket_source_address_test.dart

 // Copyright (c) 2013, 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.
 //
 
 import "dart:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
@@ skipping 25 matching lines @@
     await throws(() => connectFunction('127.0.0.1',
                                        server.port,
                                        sourceAddress: sourceAddress),
                  (e) => e is ArgumentError);
   }
   // Unsupported local address.
   for (sourceAddress in ['8.8.8.8', new InternetAddress('8.8.8.8')]) {
     await throws(() => connectFunction('127.0.0.1',
                                        server.port,
                                        sourceAddress: sourceAddress),
-                 (e) => e is SocketException);
+                 (e) => e is SocketException &&
+                     e.address == new InternetAddress('8.8.8.8'));
   }
   // Address family mismatch.
   for (sourceAddress in ['::1', InternetAddress.LOOPBACK_IP_V6]) {
     await throws(() => connectFunction('127.0.0.1',
                                        server.port,
                                        sourceAddress: sourceAddress),
                  (e) => e is SocketException);
   }
   asyncEnd();
   server.close();
@@ skipping 81 matching lines @@
       InternetAddress.ANY_IP_V4, false, Socket.connect, (s) => s.destroy());
   testConnect(
       InternetAddress.ANY_IP_V6, false, RawSocket.connect, (s) => s.close());
   testConnect(
       InternetAddress.ANY_IP_V6, false, Socket.connect, (s) => s.destroy());
   testConnect(
       InternetAddress.ANY_IP_V6, true, RawSocket.connect, (s) => s.close());
   testConnect(
       InternetAddress.ANY_IP_V6, true, Socket.connect, (s) => s.destroy());
 }