reorder repo parameters last

Many functions took the repo as their first parameter. Changing it
consistently to be the last parameter allows doing some useful things with
currying, that reduce boilerplate.

In particular, g <- gitRepo is almost never needed now, instead
use inRepo to run an IO action in the repo, and fromRepo to get
a value from the repo.

This also provides more opportunities to use monadic and applicative
combinators.

Backend.hs

@@ -47,10 +47,7 @@ orderedList = do
 			l' <- (lookupBackendName name :) <$> standard
 			Annex.changeState $ \s -> s { Annex.backends = l' }
 			return l'
-		standard = do
-			g <- gitRepo
-			return $ parseBackendList $
-				Git.configGet g "annex.backends" ""
+		standard = fromRepo $ parseBackendList . Git.configGet "annex.backends" ""
 		parseBackendList [] = list
 		parseBackendList s = map lookupBackendName $ words s
 
@@ -96,16 +93,14 @@ type BackendFile = (Maybe (Backend Annex), FilePath)
  - That can be configured on a per-file basis in the gitattributes file.
  -}
 chooseBackends :: [FilePath] -> Annex [BackendFile]
-chooseBackends fs = do
-	g <- gitRepo
-	forced <- Annex.getState Annex.forcebackend
-	if isJust forced
-		then do
+chooseBackends fs = Annex.getState Annex.forcebackend >>= go
+	where
+		go Nothing = do
+			pairs <- inRepo $ Git.checkAttr "annex.backend" fs
+			return $ map (\(f,b) -> (maybeLookupBackendName b, f)) pairs
+		go (Just _) = do
 			l <- orderedList
 			return $ map (\f -> (Just $ head l, f)) fs
-		else do
-			pairs <- liftIO $ Git.checkAttr g "annex.backend" fs
-			return $ map (\(f,b) -> (maybeLookupBackendName b, f)) pairs
 
 {- Looks up a backend by name. May fail if unknown. -}
 lookupBackendName :: String -> Backend Annex