BulletSim: Fix single physical prim reporting its mass as zero.

Properly return root mass as mass of just the root prim rather
than the mass of the linkset. SOG has the logic to add the masses
together to get the linkset mass.
Update TODO list.

OpenSim/Region/Physics/BulletSPlugin/BSPhysObject.cs

@@ -96,7 +96,8 @@ public abstract class BSPhysObject : PhysicsActor
     // Return the object mass without calculating it or having side effects
     public abstract float RawMass { get; }
     // Set the raw mass but also update physical mass properties (inertia, ...)
-    public abstract void UpdatePhysicalMassProperties(float mass);
+    // 'inWorld' true if the object has already been added to the dynamic world.
+    public abstract void UpdatePhysicalMassProperties(float mass, bool inWorld);
 
     // The last value calculated for the prim's inertia
     public OMV.Vector3 Inertia { get; set; }