Merge branch 'shindig' of https://github.com/ctiller/grpc into shindig

include/grpc++/security/auth_metadata_processor.h

include/grpc++/security/credentials.h

src/core/channel/channel_args.h

src/core/client_config/resolvers/zookeeper_resolver.c

src/core/iomgr/exec_ctx.h

src/core/iomgr/tcp_client_windows.c

src/core/iomgr/tcp_server_windows.c

src/cpp/client/secure_credentials.cc

test/cpp/end2end/end2end_test.cc