new alert while scanning

Like the old one, but does not mention which remotes are scanned.
I think this is less confusing, as it does not imply the remotes
were somehow accessed (which they are not; inaccessible remotes
can be scanned.)

Assistant/Alert.hs

@@ -240,6 +240,13 @@ commitAlert = activityAlert Nothing
 showRemotes :: [Remote] -> TenseChunk
 showRemotes = UnTensed . T.intercalate ", " . map (T.pack . Remote.name)
 
+scanAlert :: Alert
+scanAlert = baseActivityAlert
+	{ alertHeader = Just $
+		tenseWords [Tensed "Scanning" "Scanned", "for file transfers"]
+	, alertPriority = Low
+	}
+
 syncAlert :: [Remote] -> Alert
 syncAlert rs = baseActivityAlert
 	{ alertName = Just SyncAlert

Assistant/Threads/TransferScanner.hs

@@ -14,6 +14,7 @@ import Assistant.TransferQueue
 import Assistant.DaemonStatus
 import Assistant.Drop
 import Assistant.Sync
+import Assistant.Alert
 import Logs.Transfer
 import Logs.Location
 import Logs.Web (webUUID)
@@ -38,13 +39,15 @@ transferScannerThread = namedThread "TransferScanner" $ do
 	go scanned = do
 		liftIO $ threadDelaySeconds (Seconds 2)
 		(rs, infos) <- unzip <$> getScanRemote
-		if any fullScan infos || any (`S.notMember` scanned) rs
+		void $ alertWhile scanAlert $ do
-			then do
+			if any fullScan infos || any (`S.notMember` scanned) rs
-				expensiveScan rs
+				then do
-				go $ scanned `S.union` S.fromList rs
+					expensiveScan rs
-			else do
+					go $ scanned `S.union` S.fromList rs
-				mapM_ failedTransferScan rs
+				else do
-				go scanned
+					mapM_ failedTransferScan rs
+					go scanned
+			return True
 	{- All git remotes are synced, and all available remotes
 	 - are scanned in full on startup, for multiple reasons, including:
 	 -