unified the two sorting api's

MediaBrowser.Controller/Sorting/IUserBaseItemComparer.cs

@@ -0,0 +1,16 @@
+using MediaBrowser.Controller.Entities;
+
+namespace MediaBrowser.Controller.Sorting
+{
+    /// <summary>
+    /// Represents a BaseItem comparer that requires a User to perform it's comparison
+    /// </summary>
+    public interface IUserBaseItemComparer : IBaseItemComparer
+    {
+        /// <summary>
+        /// Gets or sets the user.
+        /// </summary>
+        /// <value>The user.</value>
+        User User { get; set; }
+    }
+}