Committing the Avination Scene Presence and related texture code

- Parts of region crossing code
- New bakes handling code
- Bakes now sent from sim to sim without central storage
- Appearance handling changes
- Some changes to sitting
- A number of unrelated fixes and improvements

OpenSim/Framework/IImprovedAssetCache.cs

@@ -33,6 +33,7 @@ namespace OpenSim.Framework
     {
         void Cache(AssetBase asset);
         AssetBase Get(string id);
+        bool Check(string id);
         void Expire(string id);
         void Clear();
     }