message: Add application_type
diff: @@ -188,6 +188,8 @@ private:
  CAF_TEST_FIXTURE_SCOPE(endpoint_manager_tests, fixture)
  CAF_TEST(receive) {
  + using application_type = extend<string_application>::with<
  + stream_string_application>;
  std::vector<char> read_buf(1024);
  CAF_CHECK_EQUAL(mpx->num_socket_managers(), 1u);
  auto buf = std::make_shared<std::vector<char>>();
  @@ -197,14 +199,12 @@ CAF_TEST(receive) {
  sec::unavailable_or_would_block);
  CAF_MESSAGE("adding both endpoint managers");
  auto mgr1 = make_endpoint_manager(mpx, sys, policy::scribe{sockets.first},
  - extend<string_application>::with<
  - stream_string_application>{sys, buf});
  + application_type{sys, buf});
  CAF_CHECK_EQUAL(mgr1->init(), none);
  mpx->handle_updates();
  CAF_CHECK_EQUAL(mpx->num_socket_managers(), 2u);
  auto mgr2 = make_endpoint_manager(mpx, sys, policy::scribe{sockets.second},
  - extend<string_application>::with<
  - stream_string_application>{sys, buf});
  + application_type{sys, buf});
  CAF_CHECK_EQUAL(mgr2->init(), none);
  mpx->handle_updates();
  CAF_CHECK_EQUAL(mpx->num_socket_managers(), 3u);
  