Merge github.com:grpc/grpc into optionalize_client_config

BUILD

Makefile

binding.gyp

build.yaml

config.m4

gRPC.podspec

grpc.gemspec

package.json

package.xml

src/core/lib/iomgr/ev_poll_and_epoll_posix.c

src/core/lib/iomgr/ev_poll_and_epoll_posix.h

src/core/lib/iomgr/ev_posix.c

src/core/lib/iomgr/ev_posix.h

src/core/lib/iomgr/fd_posix.c

src/core/lib/iomgr/iomgr.c

src/core/lib/iomgr/iomgr_internal.h

src/core/lib/iomgr/iomgr_posix.c

src/core/lib/iomgr/iomgr_windows.c

src/core/lib/iomgr/pollset_multipoller_with_epoll.c

src/core/lib/iomgr/pollset_multipoller_with_poll_posix.c