Added 'nodeArchiveService' bean

- Added tests around transaction visibility
 - TODO: Need to set the owner of archived and restored nodes


git-svn-id: https://svn.alfresco.com/repos/alfresco-enterprise/alfresco/HEAD/root@2786 c4b6b30b-aa2e-2d43-bbcb-ca4b014f7261

source/java/org/alfresco/repo/security/authentication/AuthenticationServiceImpl.java

@@ -109,6 +109,11 @@ public class AuthenticationServiceImpl implements AuthenticationService
             throw ae;
         }
     }
+    
+    public boolean authenticationExists(String userName)
+    {
+        return authenticationDao.userExists(userName);
+    }
 
     public String getCurrentUserName() throws AuthenticationException
     {