Implement co-operative script termination if termination comes during a script wait event (llSleep(), etc.)

This makes use of EventWaitHandles since various web references indicate that Thread.Interrupt() can also cause runtime instability.
If co-op termination is enabled, then termination sets the wait handle instead of waiting for a timeout before possibly aborting the thread.
This allows the script to cleanly terminate if it's in a llSleep/LL function delay or the next time it enters such a wait without any timeout period.
Co-op termination is not yet testable since checking for termination request within loops that never trigger a wait is not yet implemented.
This commit, unlike 1b5c41c, passes the wait handle as an extra parameter through IScript.Initialize() instead of passing IScriptInstance itself.

OpenSim/Region/Framework/Scenes/Scene.Inventory.cs

@@ -1737,6 +1737,21 @@ namespace OpenSim.Region.Framework.Scenes
         /// <param name="itemBase"></param>
         /// <returns>The part where the script was rezzed if successful.  False otherwise.</returns>
         public SceneObjectPart RezNewScript(UUID agentID, InventoryItemBase itemBase)
+        {
+            return RezNewScript(
+                agentID,
+                itemBase,
+                "default\n{\n    state_entry()\n    {\n        llSay(0, \"Script running\");\n    }\n}");
+        }
+
+        /// <summary>
+        /// Rez a new script from nothing with given script text.
+        /// </summary>
+        /// <param name="remoteClient"></param>
+        /// <param name="itemBase">Template item.</param>
+        /// <param name="scriptText"></param>
+        /// <returns>The part where the script was rezzed if successful.  False otherwise.</returns>
+        public SceneObjectPart RezNewScript(UUID agentID, InventoryItemBase itemBase, string scriptText)
         {
             // The part ID is the folder ID!
             SceneObjectPart part = GetSceneObjectPart(itemBase.Folder);
@@ -1757,9 +1772,14 @@ namespace OpenSim.Region.Framework.Scenes
                 return null;
             }
 
-            AssetBase asset = CreateAsset(itemBase.Name, itemBase.Description, (sbyte)itemBase.AssetType,
-                Encoding.ASCII.GetBytes("default\n{\n    state_entry()\n    {\n        llSay(0, \"Script running\");\n    }\n}"),
-                agentID);
+            AssetBase asset 
+                = CreateAsset(
+                    itemBase.Name, 
+                    itemBase.Description, 
+                    (sbyte)itemBase.AssetType,
+                    Encoding.ASCII.GetBytes(scriptText), 
+                    agentID);
+
             AssetService.Store(asset);
 
             TaskInventoryItem taskItem = new TaskInventoryItem();