BulletSim: add failure flag for meshing failure vs asset fetch failure

so error messages make more sense.
Change some BulletSim status log messages from WARN to INFO.
Update TODO list.

OpenSim/Region/Physics/BulletSPlugin/BSPhysObject.cs

@@ -148,7 +148,7 @@ public abstract class BSPhysObject : PhysicsActor
     // The asset state is first 'Unknown' then 'Waiting' then either 'Failed' or 'Fetched'.
     public enum PrimAssetCondition
     {
-        Unknown, Waiting, Failed, Fetched
+        Unknown, Waiting, FailedAssetFetch, FailedMeshing, Fetched
     }
     public PrimAssetCondition PrimAssetState { get; set; }