Decouple AsyncCommands from XEngine and the script instance. Make

all methods needed outside the API ststic. Async command processing
is now wholly internal to the API. This sets the stage for the next
convergence step.

OpenSim/Region/ScriptEngine/Interfaces/IScriptEngine.cs

@@ -44,7 +44,6 @@ namespace OpenSim.Region.ScriptEngine.Interfaces
     {
         Scene World { get; }
         IConfig Config { get; }
-        Object AsyncCommands { get; }
         ILog Log { get; }
         string ScriptEngineName { get; }