avoid confusing git with a modified ctime in clean filter

Linking the file to the tmp dir was not necessary in the clean
filter, and it caused the ctime to change, which caused git to think
the file was changed. This caused git status to get slow as it kept
re-cleaning unchanged files.

Command/Add.hs

@@ -115,7 +115,11 @@ start file = ifAnnexed file addpresent add
 perform :: FilePath -> CommandPerform
 perform file = do
 	lockingfile <- not <$> isDirect
-	lockDown lockingfile file >>= ingest >>= go
+	let cfg = LockDownConfig
+		{ lockingFile = lockingfile
+		, hardlinkFileTmp = True
+		}
+	lockDown cfg file >>= ingest >>= go
   where
 	go (Just key, cache) = next $ cleanup file key cache True
 	go (Nothing, _) = stop