Add --force flag to "kick user" console command to allow bypassing of recent race condition checks.

This is to allow a second attempt to remove an avatar even if "show connections" shows them as already inactive (i.e. close has already been attempted once).
You should only attempt --force if a normal kick fails.
This is partly for diagnostics as we have seen some connections occasionally remain on lbsa plaza even if they are registered as inactive.
This is not a permanent solution and may not work anyway - the ultimate solution is to stop this problem from happening in the first place.

OpenSim/Region/ClientStack/Linden/Caps/EventQueue/Tests/EventQueueTests.cs

@@ -94,7 +94,7 @@ namespace OpenSim.Region.ClientStack.Linden.Tests
             UUID spId = TestHelpers.ParseTail(0x1);
 
             SceneHelpers.AddScenePresence(m_scene, spId);
-            m_scene.IncomingCloseAgent(spId);
+            m_scene.IncomingCloseAgent(spId, false);
 
             // TODO: Add more assertions for the other aspects of event queues
             Assert.That(MainServer.Instance.GetPollServiceHandlerKeys().Count, Is.EqualTo(0));

OpenSim/Region/ClientStack/Linden/UDP/LLClientView.cs

@@ -487,16 +487,20 @@ namespace OpenSim.Region.ClientStack.LindenUDP
 
         #region Client Methods
 
-        /// <summary>
-        /// Close down the client view
-        /// </summary>
         public void Close()
+        {
+            Close(false);
+        }
+
+        public void Close(bool force)
         {
             // We lock here to prevent race conditions between two threads calling close simultaneously (e.g.
             // a simultaneous relog just as a client is being closed out due to no packet ack from the old connection.
             lock (CloseSyncLock)
             {
-                if (!IsActive)
+                // We still perform a force close inside the sync lock since this is intended to attempt close where
+                // there is some unidentified connection problem, not where we have issues due to deadlock
+                if (!IsActive && !force)
                     return;
 
                 IsActive = false;
@@ -11989,7 +11993,7 @@ namespace OpenSim.Region.ClientStack.LindenUDP
         {
             Kick(reason);
             Thread.Sleep(1000);
-            Close();
+            Disconnect();
         }
 
         public void Disconnect()