Bugfix: Direct mode no longer repeatedly checksums duplicated files.

Fixed by storing a list of cached inodes for a key, instead of just one.

Backwards compatability note: An old git-annex version will fail to parse
an inode cache file that has been written by a new version, and has
multiple items. It will succees if just one. So old git-annexes will have
even worse behavior when there are duplicated files, if that is possible.
I don't think it will be a problem. (Famous last words.)

Also, note that it doesn't expire old and unused inode caches for a key.
It would be possible to add this if needed; just look through the
associated files for a key and if there are more cached inodes, throw out
any not corresponding to associated files. Unless a file is being copied
repeatedly and the old copy deleted, this lack of expiry should not be a
problem.

Assistant/Threads/Committer.hs

@@ -297,13 +297,10 @@ handleAdds delayadd cs = returnWhen (null incomplete) $ do
 	removedKeysMap ct l = do
 		mks <- forM (filter isRmChange l) $ \c ->
 			catKeyFile $ changeFile c
-		M.fromList . catMaybes <$> forM (catMaybes mks) mkpair
+		M.fromList . concat <$> mapM mkpairs (catMaybes mks)
 	  where
-		mkpair k = do
-			mcache <- recordedInodeCache k
-			case mcache of
-				Just cache -> return $ Just (inodeCacheToKey ct cache, k)
-				Nothing -> return Nothing
+		mkpairs k = map (\c -> (inodeCacheToKey ct c, k)) <$>
+			recordedInodeCache k
 
 	failedingest = do
 		liftAnnex showEndFail