Windows: Fix some filename encoding bugs.

http://git-annex.branchable.com/bugs/Unicode_file_names_ignored_on_Windows/

Not a complete fix yet.

Annex/CatFile.hs

@@ -80,7 +80,7 @@ catKey = catKey' True
 catKey' :: Bool -> Ref -> FileMode -> Annex (Maybe Key)
 catKey' modeguaranteed ref mode
 	| isSymLink mode = do
-		l <- fromInternalGitPath . encodeW8 . L.unpack <$> get
+		l <- fromInternalGitPath . decodeBS <$> get
 		return $ if isLinkToAnnex l
 			then fileKey $ takeFileName l
 			else Nothing