Explicitly set the changed status of the prim groups affected in a delink

Mantis #2484

OpenSim/Region/Framework/Scenes/SceneGraph.cs

@@ -1690,6 +1690,7 @@ namespace OpenSim.Region.Framework.Scenes
             foreach (SceneObjectGroup g in affectedGroups)
             {
                 g.TriggerScriptChangedEvent(Changed.LINK);
+                g.HasGroupChanged = true; // Persist
                 g.ScheduleGroupForFullUpdate();
             }
         }