Added assets service method AssetsExist(), which returns whether the given list of assets exist.

This method is used to optimize sending assets with embedded assets: e.g., when a Hypergrid visitor takes an item into the inventory.

OpenSim/Services/Interfaces/IAssetService.cs

@@ -75,6 +75,13 @@ namespace OpenSim.Services.Interfaces
         /// </param>
         /// <returns>True if the id was parseable, false otherwise</returns>
         bool Get(string id, Object sender, AssetRetrieved handler);
+        
+        /// <summary>
+        /// Check if assets exist in the database.
+        /// </summary>
+        /// <param name="ids">The assets' IDs</param>
+        /// <returns>For each asset: true if it exists, false otherwise</returns>
+        bool[] AssetsExist(string[] ids);
 
         /// <summary>
         /// Creates a new asset