remove git-annex branch read cache

This cache prevented noticing changes made by another process.

The case I just ran into involved the assistant dropping a file, which
cached its presence info. Then the same file was downloaded again,
but the assistant didn't know its presence info had changed.

I don't see a way to keep this cache. Will instead rely on the OS level
file cache, for files in the journal. May need to add more higher-level
caching of info that it's ok to have a potentially stale copy of,
although much of git-annex already does so.

Annex/Branch.hs

@@ -147,7 +147,6 @@ updateTo pairs = do
 				then updateIndex branchref
 				else commitBranch branchref merge_desc
 					(nub $ fullname:refs)
-			invalidateCache
 			liftIO cleanjournal
 
 {- Gets the content of a file, which may be in the journal, or committed
@@ -168,20 +167,16 @@ getStale :: FilePath -> Annex String
 getStale = get' True
 
 get' :: Bool -> FilePath -> Annex String
-get' staleok file = fromcache =<< getCache file
+get' staleok file = fromjournal =<< getJournalFile file
 	where
-		fromcache (Just content) = return content
-		fromcache Nothing = fromjournal =<< getJournalFile file
-		fromjournal (Just content) = cache content
+		fromjournal (Just content) = return content
 		fromjournal Nothing
 			| staleok = withIndex frombranch
 			| otherwise = do
 				update
-				withIndex $ frombranch >>= cache
-		frombranch = L.unpack <$> catFile fullname file
-		cache content = do
-			setCache file content
-			return content
+				frombranch
+		frombranch = withIndex $
+			L.unpack <$> catFile fullname file
 
 {- Applies a function to modifiy the content of a file.
  -
@@ -191,11 +186,9 @@ get' staleok file = fromcache =<< getCache file
 change :: FilePath -> (String -> String) -> Annex ()
 change file a = lockJournal $ a <$> getStale file >>= set file
 
-{- Records new content of a file into the journal and cache. -}
+{- Records new content of a file into the journal -}
 set :: FilePath -> String -> Annex ()
-set file content = do
-	setJournalFile file content
-	setCache file content
+set file content = setJournalFile file content
 
 {- Stages the journal, and commits staged changes to the branch. -}
 commit :: String -> Annex ()

Annex/BranchState.hs

@@ -1,6 +1,6 @@
 {- git-annex branch state management
  -
- - Runtime state about the git-annex branch, including a small read cache.
+ - Runtime state about the git-annex branch.
  -
  - Copyright 2011-2012 Joey Hess <joey@kitenet.net>
  -
@@ -22,22 +22,6 @@ setState state = Annex.changeState $ \s -> s { Annex.branchstate = state }
 changeState :: (BranchState -> BranchState) -> Annex ()
 changeState changer = setState =<< changer <$> getState
 
-setCache :: FilePath -> String -> Annex ()
-setCache file content = changeState $ \s -> s
-	{ cachedFile = Just file, cachedContent = content}
-
-getCache :: FilePath -> Annex (Maybe String)
-getCache file = from <$> getState
-	where
-		from state
-			| cachedFile state == Just file =
-				Just $ cachedContent state
-			| otherwise = Nothing
-
-invalidateCache :: Annex ()
-invalidateCache = changeState $ \s -> s
-	{ cachedFile = Nothing, cachedContent = "" }
-
 {- Runs an action to check that the index file exists, if it's not been
  - checked before in this run of git-annex. -}
 checkIndexOnce :: Annex () -> Annex ()

Annex/Journal.hs

@@ -1,4 +1,4 @@
-{- management of the git-annex journal and cache
+{- management of the git-annex journal
  -
  - The journal is used to queue up changes before they are committed to the
  - git-annex branch. Amoung other things, it ensures that if git-annex is