Merge pull request #2645 from jtattermusch/csharp_go_beta_go

src/csharp/Grpc.Auth/GoogleCredential.cs

src/csharp/Grpc.Auth/Grpc.Auth.csproj

src/csharp/Grpc.Auth/Grpc.Auth.nuspec

src/csharp/Grpc.Auth/app.config

src/csharp/Grpc.Auth/packages.config

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

src/csharp/Grpc.Core/Credentials.cs

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

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

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

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

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

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

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

src/csharp/Grpc.Core/KeyCertificatePair.cs

src/csharp/Grpc.Core/ServerCallContext.cs

src/csharp/Grpc.Core/ServerCredentials.cs

.../Grpc.Examples.MathClient/Grpc.Examples.MathClient.csproj

.../Grpc.Examples.MathServer/Grpc.Examples.MathServer.csproj

...ationTesting.Client/Grpc.IntegrationTesting.Client.csproj