In co-op termination, extend EventWaitHandle to give this an indefinite lifetime in order to avoid a later RemotingException if scripts are being loaded into their own domains.

This is necessary because XEngineScriptBase now retains a reference to an EventWaitHandle when co-op termination is active.
Aims to address http://opensimulator.org/mantis/view.php?id=6634

OpenSim/Region/ScriptEngine/Shared/Instance/ScriptInstance.cs

@@ -241,7 +241,7 @@ namespace OpenSim.Region.ScriptEngine.Shared.Instance
             if (Engine.Config.GetString("ScriptStopStrategy", "abort") == "co-op")
             {
                 m_coopTermination = true;
-                m_coopSleepHandle = new AutoResetEvent(false);
+                m_coopSleepHandle = new XEngineEventWaitHandle(false, EventResetMode.AutoReset);
             }
         }
 
@@ -1201,4 +1201,23 @@ namespace OpenSim.Region.ScriptEngine.Shared.Instance
             Suspended = false;
         }
     }
+
+    /// <summary>
+    /// Xengine event wait handle.
+    /// </summary>
+    /// <remarks>
+    /// This class exists becase XEngineScriptBase gets a reference to this wait handle.  We need to make sure that
+    /// when scripts are running in different AppDomains the lease does not expire.
+    /// FIXME: Like LSL_Api, etc., this effectively leaks memory since the GC will never collect it.  To avoid this,
+    /// proper remoting sponsorship needs to be implemented across the board.
+    /// </remarks>
+    public class XEngineEventWaitHandle : EventWaitHandle
+    {
+        public XEngineEventWaitHandle(bool initialState, EventResetMode mode) : base(initialState, mode) {}
+
+        public override Object InitializeLifetimeService()
+        {
+            return null;
+        }
+    }
 }