started converting Ref from String to ByteString

This should make code that reads shas and refs from git faster.

Does not compile yet, a lot needs to be done still.

Git/Types.hs

@@ -81,10 +81,10 @@ instance IsString ConfigValue where
 type RemoteName = String
 
 {- A git ref. Can be a sha1, or a branch or tag name. -}
-newtype Ref = Ref String
+newtype Ref = Ref S.ByteString
 	deriving (Eq, Ord, Read, Show)
 
-fromRef :: Ref -> String
+fromRef :: Ref -> S.ByteString
 fromRef (Ref s) = s
 
 {- Aliases for Ref. -}