fix transfers of key with no associated file

Several places assumed this would not happen, and when the AssociatedFile
was Nothing, did nothing.

As part of this, preferred content checks pass the Key around.

Note that checkMatcher is sometimes now called with Just Key and Just File.
It currently constructs a FileMatcher, ignoring the Key. However, if it
constructed a FileKeyMatcher, which contained both, then it might be
possible to speed up parts of Limit, which currently call the somewhat
expensive lookupFileKey to get the Key.

I have not made this optimisation yet, because I am not sure if the key is
always the same. Will need some significant checking to satisfy myself
that's the case..

Assistant/TransferSlots.hs

@@ -103,8 +103,8 @@ runTransferThread' program batchmaker d run = go
 {- By the time this is called, the daemonstatus's currentTransfers map should
  - already have been updated to include the transfer. -}
 genTransfer :: Transfer -> TransferInfo -> TransferGenerator
-genTransfer t info = case (transferRemote info, associatedFile info) of
-	(Just remote, Just file) 
+genTransfer t info = case transferRemote info of
+	Just remote 
 		| Git.repoIsLocalUnknown (Remote.repo remote) -> do
 			-- optimisation for removable drives not plugged in
 			liftAnnex $ recordFailedTransfer t info
@@ -114,7 +114,7 @@ genTransfer t info = case (transferRemote info, associatedFile info) of
 			( do
 				debug [ "Transferring:" , describeTransfer t info ]
 				notifyTransfer
-				return $ Just (t, info, go remote file)
+				return $ Just (t, info, go remote)
 			, do
 				debug [ "Skipping unnecessary transfer:",
 					describeTransfer t info ]
@@ -149,10 +149,12 @@ genTransfer t info = case (transferRemote info, associatedFile info) of
 	 - usual cleanup. However, first check if something else is
 	 - running the transfer, to avoid removing active transfers.
 	 -}
-	go remote file transferrer = ifM (liftIO $ performTransfer transferrer t $ associatedFile info)
+	go remote transferrer = ifM (liftIO $ performTransfer transferrer t $ associatedFile info)
 		( do
-			void $ addAlert $ makeAlertFiller True $
-				transferFileAlert direction True file
+			maybe noop
+				(void . addAlert . makeAlertFiller True 
+					. transferFileAlert direction True)
+				(associatedFile info)
 			unless isdownload $
 				handleDrops
 					("object uploaded to " ++ show remote)
@@ -188,11 +190,11 @@ genTransfer t info = case (transferRemote info, associatedFile info) of
 shouldTransfer :: Transfer -> TransferInfo -> Annex Bool
 shouldTransfer t info
 	| transferDirection t == Download =
-		(not <$> inAnnex key) <&&> wantGet True file
+		(not <$> inAnnex key) <&&> wantGet True (Just key) file
 	| transferDirection t == Upload = case transferRemote info of
 		Nothing -> return False
 		Just r -> notinremote r
-			<&&> wantSend True file (Remote.uuid r)
+			<&&> wantSend True (Just key) file (Remote.uuid r)
 	| otherwise = return False
   where
 	key = transferKey t