reacting to HttpAbstractions/pull/455 and PR comments

Author: JunTaoLuo

src/Microsoft.AspNet.Server.Kestrel/Http/ListenerContext.cs

@@ -1,7 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using Microsoft.AspNet.Builder;
+using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Server.Kestrel.Infrastructure;
 
 namespace Microsoft.AspNet.Server.Kestrel.Http

src/Microsoft.AspNet.Server.Kestrel/Http/ListenerPrimary.cs

@@ -4,7 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Threading.Tasks;
-using Microsoft.AspNet.Builder;
+using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Server.Kestrel.Infrastructure;
 using Microsoft.AspNet.Server.Kestrel.Networking;
 using Microsoft.Extensions.Logging;

src/Microsoft.AspNet.Server.Kestrel/Http/ListenerSecondary.cs

@@ -4,7 +4,7 @@
 using System;
 using System.Runtime.InteropServices;
 using System.Threading.Tasks;
-using Microsoft.AspNet.Builder;
+using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Server.Kestrel.Infrastructure;
 using Microsoft.AspNet.Server.Kestrel.Networking;
 using Microsoft.Extensions.Logging;

src/Microsoft.AspNet.Server.Kestrel/KestrelEngine.cs

@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using Microsoft.AspNet.Builder;
+using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Server.Kestrel.Http;
 using Microsoft.AspNet.Server.Kestrel.Networking;
 

src/Microsoft.AspNet.Server.Kestrel/KestrelServer.cs

@@ -3,7 +3,6 @@
 
 using System;
 using System.Collections.Generic;
-using Microsoft.AspNet.Builder;
 using Microsoft.AspNet.Hosting;
 using Microsoft.AspNet.Hosting.Server;
 using Microsoft.AspNet.Http;
@@ -13,7 +12,7 @@
 
 namespace Microsoft.AspNet.Server.Kestrel
 {
-    internal class KestrelServer : IServer
+    public class KestrelServer : IServer
     {
         private Stack<IDisposable> _disposables;
         private readonly IApplicationLifetime _applicationLifetime;

test/Microsoft.AspNet.Server.KestrelTests/TestServer.cs

@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using Microsoft.AspNet.Builder;
+using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Server.Kestrel;
 
 namespace Microsoft.AspNet.Server.KestrelTests