only show latest warning, rather than combining warning alerts

In the case of the inotify limit warning, particularly, if it happens once
it will be happening repeatedly, and so combining alerts resulted in a
much too large alert message that took up a lot of memory and was too
large for the webapp to display.

Assistant/Alert.hs

@@ -66,7 +66,7 @@ warningAlert name msg = Alert
 	, alertClosable = True
 	, alertPriority = High
 	, alertIcon = Just ErrorIcon
-	, alertCombiner = Just $ dataCombiner (++)
+	, alertCombiner = Just $ dataCombiner $ \_old new -> new
 	, alertName = Just $ WarningAlert name
 	, alertButton = Nothing
 	}