Merge github.com:grpc/grpc into we-dont-need-no-backup

BUILD

Makefile

README.md

build.json

doc/connection-backoff.md

doc/interop-test-descriptions.md

include/grpc/support/port_platform.h

include/grpc/support/subprocess.h

include/grpc/support/tls.h

include/grpc/support/tls_pthread.h

src/core/security/security_connector.c

src/core/support/subprocess_posix.c

src/core/support/tls_pthread.c

src/core/tsi/ssl_transport_security.c

src/core/tsi/ssl_transport_security.h

src/core/tsi/transport_security.c

src/core/tsi/transport_security.h

src/core/tsi/transport_security_interface.h

src/csharp/.gitignore

src/csharp/EXPERIMENTAL-ONLY