Add a QueryItem method to the inventory subsystem. Currently implemented for

MySQL only, stubs for the others. This allows updating the cache with a single
item from the database.

OpenSim/Data/IInventoryData.cs

@@ -108,6 +108,12 @@ namespace OpenSim.Data
         /// <param name="item"></param>
         void deleteInventoryItem(UUID item);
 
+        /// <summary>
+        ///
+        /// </summary>
+        /// <param name="item"></param>
+        InventoryItemBase queryInventoryItem(UUID item);
+
         /// <summary>
         /// Adds a new folder specified by folder
         /// </summary>