Verify protobuf versions

There is a small possibility that the protobuf versions mismatched (in a
very messed up compilation environment where the header and the
installed library versions don't match).

src/cactus_rt/app.cc

@@ -28,6 +28,10 @@ App::App(std::string name, AppConfig config)
     SetDefaultLogFormat(logger_config_);
   }
 
+#ifdef CACTUS_RT_TRACING_ENABLED
+  GOOGLE_PROTOBUF_VERIFY_VERSION;
+#endif
+
   // TODO: backend_thread_notification_handler can throw - we need to handle this somehow
   // logger_config_.backend_thread_notification_handler
 }