stream through proxy when using fileRetriever

The problem was that when the proxy requests a key be retrieved to its
own temp file, fileRetriever was retriving it to the key's temp
location, and then moving it at the end, which broke streaming.

So, plumb through the path where the key is being retrieved to.

Remote/Directory/LegacyChunked.hs

@@ -98,7 +98,7 @@ store repotop chunksize finalizer k b p = storeHelper repotop finalizer k $ \des
  - :/ This is legacy code..
  -}
 retrieve :: (RawFilePath -> Key -> [RawFilePath]) -> RawFilePath -> Retriever
-retrieve locations d basek p miv c = withOtherTmp $ \tmpdir -> do
+retrieve locations d basek p _dest miv c = withOtherTmp $ \tmpdir -> do
 	showLongNote "This remote uses the deprecated chunksize setting. So this will be quite slow."
 	let tmp = tmpdir P.</> keyFile basek <> ".directorylegacy.tmp"
 	let tmp' = fromRawFilePath tmp
@@ -110,7 +110,7 @@ retrieve locations d basek p miv c = withOtherTmp $ \tmpdir -> do
 		b <- liftIO $ L.readFile tmp'
 		liftIO $ removeWhenExistsWith R.removeLink tmp
 		sink b
-	byteRetriever go basek p miv c
+	byteRetriever go basek p tmp miv c
 
 checkKey :: RawFilePath -> (RawFilePath -> Key -> [RawFilePath]) -> Key -> Annex Bool
 checkKey d locations k = liftIO $