kie-issues#270: DMN Runner execution identifies wrongly missing requi…

…rements

Closes: apache/incubator-kie-issues#270

The problem was not in the DMN Runne rui component but in the engine that executes the validation. The mechanism for storing messages contained a bug.
```
    @OverRide
    public DMNMessage addMessage(DMNMessage newMessage) {
        for( DMNMessage existingMessage : messages ) {
            if( isDuplicate( existingMessage, newMessage ) ) {
                return existingMessage;
            }
        }
        this.messages.add( newMessage );
        return newMessage;
    }
```

`isDuplicate` didn't take into account all needed attributes of the `message`

kie-dmn/kie-dmn-core/src/main/java/org/kie/dmn/core/util/DefaultDMNMessagesManager.java

@@ -19,6 +19,7 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Objects;
 import java.util.stream.Collectors;
 
 import org.kie.api.io.Resource;
@@ -100,7 +101,8 @@ public DMNMessage addMessage(DMNMessage.Severity severity, String message, DMNMe
 
     private boolean isDuplicate(DMNMessage existingMsg, DMNMessage newMessage) {
         return existingMsg.getMessageType().equals( newMessage.getMessageType() ) &&
-               existingMsg.getSourceReference() == newMessage.getSourceReference();
+               existingMsg.getSourceReference() == newMessage.getSourceReference() &&
+               Objects.equals(existingMsg.getText(),  newMessage.getText());
     }
 
 }