message: Fix unit tests: forced_* messages are anonymous
diff: @@ -272,7 +272,7 @@ CAF_TEST(delayed_depth_2_pipeline_50_items) {
  expect((string), from(self).to(src).with("numbers.txt"));
  expect((open_stream_msg), from(self).to(snk));
  disallow((upstream_msg::ack_open), from(snk).to(src));
  - disallow((upstream_msg::forced_drop), from(snk).to(src));
  + disallow((upstream_msg::forced_drop), from(_).to(src));
  CAF_MESSAGE("send 'ok' to trigger sink to handle open_stream_msg");
  self->send(snk, ok_atom::value);
  expect((ok_atom), from(self).to(snk));
  @@ -324,7 +324,7 @@ CAF_TEST(depth_2_pipeline_error_during_handshake) {
  self->send(snk * src, "numbers.txt");
  expect((std::string), from(self).to(src).with("numbers.txt"));
  expect((open_stream_msg), from(self).to(snk));
  - expect((upstream_msg::forced_drop), from(snk).to(src));
  + expect((upstream_msg::forced_drop), from(_).to(src));
  expect((error), from(snk).to(self).with(sec::stream_init_failed));
  }
  @@ -343,7 +343,7 @@ CAF_TEST(depth_2_pipeline_error_at_source) {
  expect((downstream_msg::batch), from(src).to(snk));
  expect((exit_msg), from(self).to(src));
  CAF_MESSAGE("expect close message from src and then result from snk");
  - expect((downstream_msg::forced_close), from(src).to(snk));
  + expect((downstream_msg::forced_close), from(_).to(snk));
  }
  CAF_TEST(depth_2_pipelin_error_at_sink) {
  @@ -360,7 +360,7 @@ CAF_TEST(depth_2_pipelin_error_at_sink) {
  expect((upstream_msg::ack_open), from(snk).to(src));
  expect((exit_msg), from(self).to(snk));
  CAF_MESSAGE("expect close and result messages from snk");
  - expect((upstream_msg::forced_drop), from(snk).to(src));
  + expect((upstream_msg::forced_drop), from(_).to(src));
  }
  CAF_TEST(depth_3_pipeline_50_items) {
  