Allow the ServerContext to be Unwrapped Programmatically

        public void deleteContext(ServerContext serverContext, TProtocol input, TProtocol output) {
          ...
          ThriftCLIServerContext context = (ThriftCLIServerContext) serverContext;
}

        public void deleteContext(ServerContext serverContext, TProtocol input, TProtocol output) {
          ...
          ThriftCLIServerContext context = serverContext.unwrap(ThriftCLIServerContext.class);
}