Merge pull request #1504 from jtattermusch/csharp_api_fixes

src/csharp/Grpc.Core.Tests/ClientServerTest.cs

src/csharp/Grpc.Core.Tests/ServerTest.cs

src/csharp/Grpc.Core/AsyncClientStreamingCall.cs

src/csharp/Grpc.Core/AsyncDuplexStreamingCall.cs

src/csharp/Grpc.Core/AsyncServerStreamingCall.cs

src/csharp/Grpc.Core/Call.cs

src/csharp/Grpc.Core/Calls.cs

src/csharp/Grpc.Core/Grpc.Core.csproj

src/csharp/Grpc.Core/IAsyncStreamReader.cs

src/csharp/Grpc.Core/IAsyncStreamWriter.cs

src/csharp/Grpc.Core/IClientStreamWriter.cs

src/csharp/Grpc.Core/IServerStreamWriter.cs

src/csharp/Grpc.Core/Internal/AsyncCallServer.cs

src/csharp/Grpc.Core/Internal/ClientRequestStream.cs

src/csharp/Grpc.Core/Internal/ClientResponseStream.cs

src/csharp/Grpc.Core/Internal/ServerCallHandler.cs

src/csharp/Grpc.Core/Internal/ServerCalls.cs

src/csharp/Grpc.Core/Internal/ServerRequestStream.cs

src/csharp/Grpc.Core/Internal/ServerResponseStream.cs

src/csharp/Grpc.Core/Server.cs