merge with head

BUILD

Makefile

build.json

doc/interop-test-descriptions.md

include/grpc++/client_context.h

include/grpc++/server_context.h

include/grpc++/stream.h

include/grpc++/stub_options.h

include/grpc/grpc.h

src/compiler/cpp_generator.cc

src/compiler/csharp_generator.cc

src/core/channel/client_channel.c

src/core/surface/call.c

src/core/surface/call.h

src/core/surface/channel.c

src/core/surface/completion_queue.c

src/core/surface/server.c

src/cpp/client/channel.cc

src/cpp/client/client_context.cc

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