Add regression test for inventory item give, reject and subsequent trash folder purge by receiver.

This commit also actually adds the InventoryTransferModuleTests file which I previously forgot

OpenSim/Tests/Common/Mock/TestClient.cs

@@ -61,6 +61,7 @@ namespace OpenSim.Tests.Common.Mock
         // Test client specific events - for use by tests to implement some IClientAPI behaviour.
         public event Action<RegionInfo, Vector3, Vector3> OnReceivedMoveAgentIntoRegion;
         public event Action<ulong, IPEndPoint> OnTestClientInformClientOfNeighbour;
+        public event Action<GridInstantMessage> OnReceivedInstantMessage;
 
 // disable warning: public events, part of the public API
 #pragma warning disable 67
@@ -550,7 +551,8 @@ namespace OpenSim.Tests.Common.Mock
 
         public void SendInstantMessage(GridInstantMessage im)
         {
-
+            if (OnReceivedInstantMessage != null)
+                OnReceivedInstantMessage(im);
         }
 
         public void SendGenericMessage(string method, UUID invoice, List<string> message)