object put: Made output (almost) match original output

(The file path is omitted, but since only one object can be added at a time, I think this is ok)

core/commands2/object.go

@@ -224,7 +224,7 @@ Data should be in the format specified by <encoding>.
 	Marshalers: cmds.MarshalerMap{
 		cmds.Text: func(res cmds.Response) ([]byte, error) {
 			object := res.Output().(*Object)
-			return []byte(object.Hash), nil
+			return []byte("added " + object.Hash), nil
 		},
 	},
 	Type: &Object{},