record transfer information on local git remotes

In order to record a semi-useful filename associated with the key,
this required plumbing the filename all the way through to the remotes'
storeKey and retrieveKeyFile.

Note that there is potential for deadlock here, narrowly avoided.
Suppose the repos are A and B. A sends file foo to B, and at the same
time, B gets file foo from A. So, A locks its upload transfer info file,
and then locks B's download transfer info file. At the same time,
B is taking the two locks in the opposite order. This is only not a
deadlock because the lock code does not wait, and aborts. So one of A or
B's transfers will be aborted and the other transfer will continue.
Whew!

Remote/S3.hs

@@ -113,8 +113,8 @@ s3Setup u c = handlehost $ M.lookup "host" c
 					-- be human-readable
 					M.delete "bucket" defaults
 
-store :: Remote -> Key -> Annex Bool
-store r k = s3Action r False $ \(conn, bucket) -> do
+store :: Remote -> Key -> AssociatedFile -> Annex Bool
+store r k _f = s3Action r False $ \(conn, bucket) -> do
 	dest <- inRepo $ gitAnnexLocation k
 	res <- liftIO $ storeHelper (conn, bucket) r k dest
 	s3Bool res
@@ -149,12 +149,12 @@ storeHelper (conn, bucket) r k file = do
 		xheaders = filter isxheader $ M.assocs $ fromJust $ config r
 		isxheader (h, _) = "x-amz-" `isPrefixOf` h
 
-retrieve :: Remote -> Key -> FilePath -> Annex Bool
-retrieve r k f = s3Action r False $ \(conn, bucket) -> do
+retrieve :: Remote -> Key -> AssociatedFile -> FilePath -> Annex Bool
+retrieve r k _f d = s3Action r False $ \(conn, bucket) -> do
 	res <- liftIO $ getObject conn $ bucketKey r bucket k
 	case res of
 		Right o -> do
-			liftIO $ L.writeFile f $ obj_data o
+			liftIO $ L.writeFile d $ obj_data o
 			return True
 		Left e -> s3Warning e