use ByteStrings when reading annex symlinks and pointers

Now there's a ByteString used all the way from disk to Key.

The main complication in this conversion was the use of fromInternalGitPath
in several places to munge things on Windows. The things that used that
were changed to parse the ByteString using either path separator.

Also some code that had read from files to a String lazily was changed
to read a minimal strict ByteString.

Command/Fsck.hs

@@ -205,8 +205,7 @@ performKey key backend numcopies = do
 check :: [Annex Bool] -> Annex Bool
 check cs = and <$> sequence cs
 
-{- Checks that symlinks points correctly to the annexed content.
- -}
+{- Checks that symlinks points correctly to the annexed content. -}
 fixLink :: Key -> FilePath -> Annex Bool
 fixLink key file = do
 	want <- calcRepo $ gitAnnexLink file key
@@ -215,7 +214,7 @@ fixLink key file = do
 	return True
   where
 	go want have
-		| want /= fromInternalGitPath have = do
+		| want /= fromInternalGitPath (fromRawFilePath have) = do
 			showNote "fixing link"
 			liftIO $ createDirectoryIfMissing True (parentDir file)
 			liftIO $ removeFile file
@@ -562,7 +561,7 @@ badContentDirect file key = do
 badContentRemote :: Remote -> FilePath -> Key -> Annex String
 badContentRemote remote localcopy key = do
 	bad <- fromRepo gitAnnexBadDir
-	let destbad = bad </> fileKey key
+	let destbad = bad </> keyFile key
 	movedbad <- ifM (inAnnex key <||> liftIO (doesFileExist destbad))
 		( return False
 		, do