avoid too long temp dir template

The filename might be at or close to the filename length limit, so using it
as the template for the temp dir would then fail.

Annex/ReplaceFile.hs

@@ -27,7 +27,8 @@ replaceFile :: FilePath -> (FilePath -> Annex ()) -> Annex ()
 replaceFile file action = do
 	misctmpdir <- fromRepo gitAnnexTmpMiscDir
 	void $ createAnnexDirectory misctmpdir
-	let basetmp = takeFileName file
+	filemax <- liftIO $ fileNameLengthLimit misctmpdir
+	let basetmp = take (filemax `div` 2) (takeFileName file)
 	withTmpDirIn misctmpdir basetmp $ \tmpdir -> do
 		let tmpfile = tmpdir <> basetmp
 		action tmpfile