v5 for direct mode, with automatic upgrade

This includes storing the current state of the HEAD ref, which git annex
sync is going to need, but does not make sync use it.

Config.hs

@@ -71,14 +71,6 @@ getNumCopies Nothing = annexNumCopies <$> Annex.getGitConfig
 isDirect :: Annex Bool
 isDirect = annexDirect <$> Annex.getGitConfig
 
-setDirect :: Bool -> Annex ()
-setDirect b = do
-	setConfig (annexConfig "direct") val
-	setConfig (ConfigKey Git.Config.coreBare) val
-	Annex.changeGitConfig $ \c -> c { annexDirect = b }
-  where
-	val = Git.Config.boolConfig b
-
 crippledFileSystem :: Annex Bool
 crippledFileSystem = annexCrippledFileSystem <$> Annex.getGitConfig