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.

Annex/Direct.hs

@@ -52,8 +52,8 @@ stageDirect = do
 				 - it really was. -}
 				oldcache <- recordedInodeCache key
 				case oldcache of
-					Nothing -> modifiedannexed file key cache
-					Just c -> unlessM (compareInodeCaches c cache) $
+					[] -> modifiedannexed file key cache
+					_ -> unlessM (elemInodeCaches cache oldcache) $
 						modifiedannexed file key cache
 			(Just key, Nothing, _) -> deletedannexed file key
 			(Nothing, Nothing, _) -> deletegit file
@@ -87,11 +87,11 @@ addDirect file cache = do
 	got Nothing = do
 		showEndFail
 		return False
-	got (Just (key, _)) = ifM (sameInodeCache file $ Just cache)
+	got (Just (key, _)) = ifM (sameInodeCache file [cache])
 		( do
 			l <- inRepo $ gitAnnexLink file key
 			stageSymlink file =<< hashSymlink l
-			writeInodeCache key cache
+			addInodeCache key cache
 			void $ addAssociatedFile key file
 			logStatus key InfoPresent
 			showEndOk