Handle OAuth2 AuthorizationExceptions in pub.

BUG=6950

Review URL: https://codereview.chromium.org//11416352

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@15747 260f80e4-7a28-3924-810f-c04153c831b5
diff --git a/lib/src/client.dart b/lib/src/client.dart
index eb7b062..a397c00 100644
--- a/lib/src/client.dart
+++ b/lib/src/client.dart
@@ -96,15 +96,15 @@
 
       var authenticate;
       try {
-        authenticate = parseAuthenticateHeader(
+        authenticate = new AuthenticateHeader.parse(
             response.headers['www-authenticate']);
       } on FormatException catch (e) {
         return response;
       }
 
-      if (authenticate.first != 'bearer') return response;
+      if (authenticate.scheme != 'bearer') return response;
 
-      var params = authenticate.last;
+      var params = authenticate.parameters;
       if (!params.containsKey('error')) return response;
 
       throw new AuthorizationException(