Merge remote-tracking branch 'upstream/master' into proto_db

.gitmodules

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

composer.json

config.m4

doc/PROTOCOL-HTTP2.md

doc/core/pending_api_cleanups.md

doc/environment_variables.md

etc/roots.pem

examples/node/static_codegen/greeter_client.js

examples/ruby/route_guide/route_guide_client.rb

examples/ruby/route_guide/route_guide_server.rb

gRPC-Core.podspec

grpc.gemspec

include/grpc++/create_channel_posix.h

include/grpc++/ext/reflection.grpc.pb.h

include/grpc++/ext/reflection.pb.h