Adds TLS support to the ObjC library, and tests against the remote gRPC server

Remove an extra unref

remove opts param from signature

minor fix in TLS error message

add missing defines on windows (WIN64)

partial fix for #546

Less verbose logs on windows

Command:
protoc --plugin=/usr/local/bin/protoc-gen-objc test.proto
messages.proto empty.proto
--proto_path=/Users/jcanizales/git/protobuf-objc/src/compiler
--proto_path=. --objc_out="./"

Avoid writing build.json during a test.

allow empty messages in gRPC on windows

Merge branch 'php_basestub_metadata_callback' of github.com:stanley-cheung/grpc into php_basestub_metadata_callback