ok, let's just use extensible-exceptions

Backend.hs

@@ -27,7 +27,7 @@ module Backend (
 ) where
 
 import Control.Monad.State
-import Control.Exception
+import Control.Exception.Extensible
 import System.Directory
 import System.FilePath
 import Data.String.Utils
@@ -39,7 +39,6 @@ import qualified Annex
 import Utility
 import Types
 import qualified TypeInternals as Internals
-import Portability
 
 {- List of backends in the order to try them when storing a new key. -}
 list :: Annex [Backend]

Portability.hs

@@ -1,16 +0,0 @@
-{- git-annex - Nasty portability workarounds. -}
-module Portability (SomeException) where
-
-import Control.Exception
-
--- old ghc does not know about SomeException. 
---
--- http://haskell.1045720.n5.nabble.com/Help-using-catch-in-6-10-td3127921.html#a3127921
---
--- This needs ghc -cpp
---
--- This would be better, but then users of old ghc would need to install it.
--- http://hackage.haskell.org/package/extensible-exceptions
-#if __GLASGOW_HASKELL__ < 610
-type SomeException = Exception 
-#endif 

Remotes.hs

@@ -17,7 +17,7 @@ module Remotes (
 ) where
 
 import IO (bracket_)
-import Control.Exception hiding (bracket_)
+import Control.Exception.Extensible hiding (bracket_)
 import Control.Monad.State (liftIO)
 import Control.Monad (filterM)
 import qualified Data.Map as Map
@@ -40,7 +40,6 @@ import Locations
 import UUID
 import Utility
 import qualified Core
-import Portability
 
 {- Human visible list of remotes. -}
 list :: [Git.Repo] -> String