addurl, importfeed: Honor annex.diskreserve as long as the size of the url can be checked.

This adds a http HEAD before the download is done. That was already the
case when the assistant was running, and it seems worth it to avoid filling
up the whole disk, like happened to my server today.

Command/AddUrl.hs

@@ -28,7 +28,6 @@ import Config
 import Annex.Content.Direct
 import Logs.Location
 import qualified Logs.Transfer as Transfer
-import Utility.Daemon (checkDaemon)
 #ifdef WITH_QUVI
 import Annex.Quvi
 import qualified Utility.Quvi as Quvi
@@ -153,44 +152,40 @@ addUrlFile relaxed url file = do
 download :: URLString -> FilePath -> Annex Bool
 download url file = do
 	dummykey <- genkey
-	tmp <- fromRepo $ gitAnnexTmpLocation dummykey
-	showOutput
-	ifM (runtransfer dummykey tmp)
-		( do
-			backend <- chooseBackend file
-			let source = KeySource
-				{ keyFilename = file
-				, contentLocation = tmp
-				, inodeCache = Nothing
-				}
-			k <- genKey source backend
-			case k of
-				Nothing -> return False
-				Just (key, _) -> cleanup url file key (Just tmp)
-		, return False
-		)
+	prepGetViaTmpChecked dummykey $ do
+		tmp <- fromRepo $ gitAnnexTmpLocation dummykey
+		showOutput
+		ifM (runtransfer dummykey tmp)
+			( do
+				backend <- chooseBackend file
+				let source = KeySource
+					{ keyFilename = file
+					, contentLocation = tmp
+					, inodeCache = Nothing
+					}
+				k <- genKey source backend
+				case k of
+					Nothing -> return False
+					Just (key, _) -> cleanup url file key (Just tmp)
+			, return False
+			)
   where
 	{- Generate a dummy key to use for this download, before we can
 	 - examine the file and find its real key. This allows resuming
 	 - downloads, as the dummy key for a given url is stable.
 	 -
-	 - If the assistant is running, actually hits the url here,
-	 - to get the size, so it can display a pretty progress bar.
+	 - Actually hits the url here, to get the size. This is needed to
+	 - avoid exceeding the diskreserve, and so the assistant can 
+	 - display a pretty progress bar.
 	 -}
 	genkey = do
-		pidfile <- fromRepo gitAnnexPidFile
-		size <- ifM (liftIO $ isJust <$> checkDaemon pidfile)
-			( do
-				headers <- getHttpHeaders
-				snd <$> Url.withUserAgent (Url.exists url headers)
-			, return Nothing
-			)
+		headers <- getHttpHeaders
+		size <- snd <$> Url.withUserAgent (Url.exists url headers)
 		Backend.URL.fromUrl url size
   	runtransfer dummykey tmp = 
 		Transfer.download webUUID dummykey (Just file) Transfer.forwardRetry $ const $ do
 			liftIO $ createDirectoryIfMissing True (parentDir tmp)
 			downloadUrl [url] tmp
-		
 
 cleanup :: URLString -> FilePath -> Key -> Maybe FilePath -> Annex Bool
 cleanup url file key mtmp = do