make Annex an opaque data type

Was a type alias; using newtype has the benefit that type errors will
show "Annex foo" rather than two lines of internal type nonsense. Yay!
There should be no other effects to size or runtime.

I've tried to do this at least twice before (each time I read RWH chapter 10);
finally understood how to this time.. sorta.

Annex.hs

@@ -5,6 +5,8 @@
  - Licensed under the GNU GPL version 3 or higher.
  -}
 
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+
 module Annex (
 	Annex,
 	AnnexState(..),
@@ -17,6 +19,7 @@ module Annex (
 ) where
 
 import Control.Monad.State
+import Control.Monad.IO.Control
 
 import qualified Git
 import Git.Queue
@@ -28,7 +31,14 @@ import Types.TrustLevel
 import Types.UUID
 
 -- git-annex's monad
-type Annex = StateT AnnexState IO
+newtype Annex a = Annex { runAnnex :: StateT AnnexState IO a }
+	deriving (
+		Functor,
+		Monad,
+		MonadIO,
+		MonadControlIO,
+		MonadState AnnexState
+	)
 
 -- internal state storage
 data AnnexState = AnnexState
@@ -78,9 +88,9 @@ new gitrepo = newState `liftM` (liftIO . Git.configRead) gitrepo
 
 {- performs an action in the Annex monad -}
 run :: AnnexState -> Annex a -> IO (a, AnnexState)
-run = flip runStateT
+run s a = runStateT (runAnnex a) s
 eval :: AnnexState -> Annex a -> IO a
-eval = flip evalStateT
+eval s a = evalStateT (runAnnex a) s
 
 {- Gets a value from the internal state, selected by the passed value
  - constructor. -}