Alleviate an issue where calling Thread.Abort() on script WorkItems can fail to release locks, resulting in a crippled simulator.

This seems to be a particular problem with ReaderWriterLockSlim, though other locks can be affected as well.
It has been seen to happen when llDie() is called in a linkset running more than one script.
Alleviation here means supplying a ScriptInstance.Stop() timeout of 1000ms rather than 0ms, to give events a chance to complete.
Also, we check the IsRunning status at the top of the ScriptInstance.EventProcessor() so that another event doesn't start in the mean time.
Ultimately, a better solution may have to be found since a long-running event would still exceed the timeout and be aborted.

OpenSim/Region/ScriptEngine/XEngine/XEngine.cs

@@ -1118,7 +1118,11 @@ namespace OpenSim.Region.ScriptEngine.XEngine
             }
 
             instance.ClearQueue();
-            instance.Stop(0);
+
+            // Give the script some time to finish processing its last event.  Simply aborting the script thread can
+            // cause issues on mono 2.6, 2.10 and possibly later where locks are not released properly on abort.
+            instance.Stop(1000);
+            
 //                bool objectRemoved = false;
 
             lock (m_PrimObjects)