IO exception rework

ghc 7.4 comaplains about use of System.IO.Error to catch exceptions.
Ok, use Control.Exception, with variants specialized to only catch IO
exceptions.

Annex/Journal.hs

@@ -91,4 +91,4 @@ lockJournal a = do
 {- Runs an action, catching failure and running something to fix it up, and
  - retrying if necessary. -}
 doRedo :: IO a -> IO b -> IO a
-doRedo a b = catch a $ const $ b >> a
+doRedo a b = catchIO a $ const $ b >> a