Kan-Ed fix series. Fix llTakeControls to behave as documented.

XEngine fixes: prevent queue overruns, prevent spamming when no key
is down. Release controls when conflicting permissions are requested
or permissions are refused later. Release when prim or script are deleted.
Fixes Scene script instance deletion semantics.

OpenSim/Region/ScriptEngine/Interfaces/IScriptInstance.cs

@@ -93,6 +93,7 @@ namespace OpenSim.Region.ScriptEngine.Interfaces
         DetectParams GetDetectParams(int idx);
         UUID GetDetectID(int idx);
         void SaveState(string assembly);
+        void DestroyScriptInstance();
 
         IScriptApi GetApi(string name);
     }