/**
    * Checks whether the specified annotation is a valid constraint annotation. A constraint annotations has to
    * fulfill the following conditions:
    * <ul>
    * <li>Has to contain a <code>ConstraintValidator</code> implementation.</li>
    * <li>Defines a message parameter.</li>
    * <li>Defines a group parameter.</li>
    * <li>Defines a payload parameter.</li>
    * </ul>
    *
    * @param annotation The annotation to test.
    *
    * @return <code>true</code> if the annotation fulfills the above condtions, <code>false</code> otherwise.
    */
   public boolean isConstraintAnnotation(Annotation annotation)