Add coalesced scene objects class and serializer. This is currently only used by the TestRezCoalescedObject() regression test.

This structure matches the existing one for SceneObjects and will allow code to be reused by the uuid gatherer, other tests, etc.
Test is not yet fully implemented due to a bug in rezzing coalesced objects where they all get the same name as the item.
Only one object should get the same name as the item, which appears to be the one selected last when the the objects were coalesced in the first place.
This bug will be addressed shortly.

OpenSim/Region/Framework/Scenes/SceneGraph.cs

@@ -997,6 +997,8 @@ namespace OpenSim.Region.Framework.Scenes
                     {
                         foreach (SceneObjectPart p in ((SceneObjectGroup)entity).Parts)
                         {
+//                            m_log.DebugFormat("[SCENE GRAPH]: Part {0} has name {1}", p.UUID, p.Name);
+                        
                             if (p.Name == name)
                             {
                                 sop = p;