Support git's core.sharedRepository configuration

This is incomplete, it does not honor it yet for hash directories
and other annex bookkeeping files. Some of that is not needed for a bare
repo; some of it may be.

Command/Fsck.hs

@@ -166,10 +166,9 @@ verifyLocationLog key desc = do
 	-- Since we're checking that a key's file is present, throw
 	-- in a permission fixup here too.
 	when present $ do
-		f <- inRepo $ gitAnnexLocation key
-		liftIO $ do
-			preventWrite f
-			preventWrite (parentDir f)
+		file <- inRepo $ gitAnnexLocation key
+		freezeContent file
+		freezeContentDir file
 
 	u <- getUUID
 	verifyLocationLog' key desc present u (logChange key u)