RM-2045 Check that content is not re-classified.

Currently this is not supported, although it will be needed in the future.

Also take the opportunity to change the unit tests to use:
    when(x.y()).thenReturn(z));
rather than:
    doReturn(z).when(x).y();
This is because I noticed the javadoc for "doReturn" gives a good
explanation of when to use each (use the former whenever possible for
readability; use the latter if there's no choice).

+review RM-25

git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/modules/recordsmanagement/HEAD@102231 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

rm-server/source/java/org/alfresco/module/org_alfresco_module_rm/classification/ClassificationServiceImpl.java

@@ -230,6 +230,11 @@ public class ClassificationServiceImpl extends ServiceBaseImpl
         {
             throw new InvalidNode(content, "The supplied node is not a content node.");
         }
+        if (nodeService.hasAspect(content, ASPECT_CLASSIFIED))
+        {
+            throw new UnsupportedOperationException(
+                        "The content has already been classified. Reclassification is currently not supported.");
+        }
 
         Map<QName, Serializable> properties = new HashMap<QName, Serializable>();
         checkClassificationLevelId(classificationLevelId);