protobuf: apply several improvements and add an option to do build-time checks

add an option to do build-time checks
  and double the build time approximately if enabled

add a simple test

protobuf is moved to github,
  see more https://groups.google.com/d/msg/protobuf/3qvNnYo8-SM/GSMYGGBNXfoJ

provide better format
protobuf: update 2.6.1 bottle.