safer inannex checking

git-annex-shell inannex now returns always 0, 1, or 100 (the last when
it's unclear if content is currently in the index due to it currently being
moved or dropped).

(Actual locking code still not yet written.)

Remote/Bup.hs

@@ -139,17 +139,21 @@ remove _ = do
  - in a bup repository. One way it to check if the git repository has
  - a branch matching the name (as created by bup split -n).
  -}
-checkPresent :: Git.Repo -> Git.Repo -> Key -> Annex (Either IOException Bool)
+checkPresent :: Git.Repo -> Git.Repo -> Key -> Annex (Either String Bool)
 checkPresent r bupr k
 	| Git.repoIsUrl bupr = do
 		showAction $ "checking " ++ Git.repoDescribe r
 		ok <- onBupRemote bupr boolSystem "git" params
 		return $ Right ok
-	| otherwise = liftIO $ try $ boolSystem "git" $ Git.gitCommandLine params bupr
+	| otherwise = dispatch <$> localcheck
 	where
 		params = 
 			[ Params "show-ref --quiet --verify"
 			, Param $ "refs/heads/" ++ show k]
+		localcheck = liftIO $ try $
+			boolSystem "git" $ Git.gitCommandLine params bupr
+		dispatch (Left e) = Left $ show e
+		dispatch (Right v) = Right v
 
 {- Store UUID in the annex.uuid setting of the bup repository. -}
 storeBupUUID :: UUID -> BupRepo -> Annex ()