Merge github.com:grpc/grpc into an-update-on-c++

INSTALL

Makefile

build.json

include/grpc++/async_unary_call.h

include/grpc++/client_context.h

include/grpc++/impl/client_unary_call.h

include/grpc++/stream.h

include/grpc/grpc.h

src/compiler/cpp_generator.cc

src/core/iomgr/pollset_multipoller_with_epoll.c

src/core/security/credentials.c

src/core/surface/call.c

src/core/surface/channel.c

src/core/transport/chttp2_transport.c

src/core/transport/metadata.c

src/core/transport/metadata.h

src/cpp/client/client_unary_call.cc

src/csharp/GrpcApi/MathGrpc.cs

src/csharp/GrpcApi/TestServiceGrpc.cs

src/csharp/GrpcApiTests/MathClientServerTests.cs