Manage some items as single instance throughout #54

MediaBrowser.Model/Entities/IByReferenceItem.cs

@@ -0,0 +1,16 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace MediaBrowser.Model.Entities
+{
+    /// <summary>
+    /// This is a marker class that tells us that a particular item type may be physically resolved
+    /// more than once within the library and we need to be sure to resolve them all to the same
+    /// instance of that item.
+    /// </summary>
+    public interface IByReferenceItem
+    {
+    }
+}