less intrusive cache prevention.

more tests.

NzbDrone.Core/Datastore/NoCacheReferenceSystem.cs

@@ -0,0 +1,15 @@
+using System.Linq;
+using Db4objects.Db4o.Internal;
+using Db4objects.Db4o.Internal.References;
+
+namespace NzbDrone.Core.Datastore
+{
+    public class NoCacheReferenceSystem : HashcodeReferenceSystem
+    {
+        public override ObjectReference ReferenceForId(int id)
+        {
+            //never return an in memory instance of objects as query result. always go to db.
+            return null;
+        }
+    }
+}