Make example/spring-txn fail if transactions are not used

Also remove the @TxN annotation from see_message.feature, since it
fails if transactions are used.

Author: brasmusson

examples/spring-txn/src/test/java/cucumber/examples/spring/txn/UserStepdefs.java

@@ -4,6 +4,9 @@
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.test.context.ContextConfiguration;
 import org.springframework.test.context.web.WebAppConfiguration;
+import org.springframework.transaction.support.TransactionSynchronizationManager;
+
+import static org.junit.Assert.assertTrue;
 
 import java.util.List;
 
@@ -31,5 +34,7 @@ public void a_User_has_posted_the_following_messages(List<Message> messages) thr
             m.setAuthor(user);
             messageRepository.save(m);
         }
+	assertTrue("No transaction is active", 
+		   TransactionSynchronizationManager.isActualTransactionActive());
     }
 }

examples/spring-txn/src/test/resources/cucumber/examples/spring/txn/see_messages.feature

@@ -1,4 +1,3 @@
-@txn
 Feature: See Messages
 
   Scenario: See another user's messages