unify exception handling into Utility.Exception

Removed old extensible-exceptions, only needed for very old ghc.

Made webdav use Utility.Exception, to work after some changes in DAV's
exception handling.

Removed Annex.Exception. Mostly this was trivial, but note that
tryAnnex is replaced with tryNonAsync and catchAnnex replaced with
catchNonAsync. In theory that could be a behavior change, since the former
caught all exceptions, and the latter don't catch async exceptions.

However, in practice, nothing in the Annex monad uses async exceptions.
Grepping for throwTo and killThread only find stuff in the assistant,
which does not seem related.

Command.Add.undo is changed to accept a SomeException, and things
that use it for rollback now catch non-async exceptions, rather than
only IOExceptions.

Annex/ReplaceFile.hs

@@ -9,7 +9,6 @@ module Annex.ReplaceFile where
 
 import Common.Annex
 import Annex.Perms
-import Annex.Exception
 
 {- Replaces a possibly already existing file with a new version, 
  - atomically, by running an action.
@@ -31,7 +30,7 @@ replaceFileOr :: FilePath -> (FilePath -> Annex ()) -> (FilePath -> Annex ()) ->
 replaceFileOr file action rollback = do
 	tmpdir <- fromRepo gitAnnexTmpMiscDir
 	void $ createAnnexDirectory tmpdir
-	bracketAnnex (liftIO $ setup tmpdir) rollback $ \tmpfile -> do
+	bracket (liftIO $ setup tmpdir) rollback $ \tmpfile -> do
 		action tmpfile
 		liftIO $ catchIO (rename tmpfile file) (fallback tmpfile)
   where