Get "save oar" and "save iar" to tell you in a more friendly manner if the filename to save already exists, rather than exception throwing.

Also changes ConsoleUtil.CheckFileExists to CheckFileDoesNotExist() since this is more meaningful in the context, even though it does result in double negatives.

OpenSim/Server/Handlers/Asset/AssetServerConnector.cs

@@ -141,6 +141,9 @@ namespace OpenSim.Server.Handlers.Asset
             }
             
             string fileName = rawAssetId;
+
+            if (!ConsoleUtil.CheckFileDoesNotExist(MainConsole.Instance, fileName))
+                return;
             
             using (FileStream fs = new FileStream(fileName, FileMode.CreateNew))
             {