How to update the C++ sources of gRPC:

1. git clone http://github.com/grpc/grpc.git in a convenient directory
2. git checkout <tag> (current is release-0_13, commithash 78e04bbd)
3. mkdir -p third_party/grpc/src
4. cp -R <gRPC git tree>/src/{compiler,core-cpp} third_party/grpc/src
5. cp -R <gRPC git tree>/include third_party/grpc
6. Update BUILD files by copying the rules from the BUILD file of gRPC
7. Patch in grpc.patch. It makes gRPC work under msys2.

How to update the Java plugin:

1. Checkout commit a6cb001147b7a53c11516b5fdfec32aa21a1a9fa from https://github.com/grpc/grpc-java
2. cp -R <grpc-java git tree>/compiler/src/java_plugin third_party/grpc/compiler/src

How to update the Java code:

Download the necessary jars at version 1.3.0 from maven central.