add warning on add of annex link

Warn when adding a annex symlink or pointer file that uses a key that is
not known to the repository, to prevent confusion if the user has copied it
from some other repository.

This commit was sponsored by Jake Vosloo on Patreon.

Command/Smudge.hs

@@ -98,8 +98,9 @@ clean file = do
   where
 	go b = case parseLinkTargetOrPointerLazy b of
 		Just k -> do
-			getMoveRaceRecovery k file
-			liftIO $ L.hPut stdout b
+			addingExistingLink file k $ do
+				getMoveRaceRecovery k file
+				liftIO $ L.hPut stdout b
 		Nothing -> do
 			let fileref = Git.Ref.fileRef file
 			indexmeta <- catObjectMetaData fileref