avoid unnecessary log changes when re-adding the same url

Logs/Web.hs

@@ -47,6 +47,8 @@ getUrls key = go $ urlLog key : oldurlLogs key
 {- Records a change in an url for a key. -}
 setUrl :: Key -> URLString -> LogStatus -> Annex ()
 setUrl key url status = do
+	us <- getUrls key
+	unless (status == InfoPresent && url `elem` us) $ do
 		addLog (urlLog key) =<< logNow status url
 
 		-- update location log to indicate that the web has the key, or not