Introduces the message transfer module. It splits the transfer mechanics off

the IM module and makes it into a module of it's own, which can be used by
all other modules. Removes some ugly hacks. Refer to the IM module to see
how it's used. Also fixes the persistence issue (Mantis #2598)

OpenSim/Region/Environment/Scenes/SceneObjectGroup.cs

@@ -1211,6 +1211,9 @@ namespace OpenSim.Region.Environment.Scenes
         /// <param name="datastore"></param>
         public void ProcessBackup(IRegionDataStore datastore)
         {
+            if (!m_isBackedUp)
+                return;
+
             // Since this is the top of the section of call stack for backing up a particular scene object, don't let
             // any exception propogate upwards.