queue and start download of git-annex from web, using git-annex, when upgrade is started

Assistant/Threads/TransferWatcher.hs

@@ -16,6 +16,7 @@ import Utility.DirWatcher.Types
 import qualified Remote
 
 import Control.Concurrent
+import qualified Data.Map as M
 
 {- This thread watches for changes to the gitAnnexTransferDir,
  - and updates the DaemonStatus's map of ongoing transfers. -}
@@ -89,6 +90,11 @@ onDel file = case parseTransferFile file of
 		debug [ "transfer finishing:", show t]
 		minfo <- removeTransfer t
 
+		-- Run transfer hook.
+		void $ maybe noop (\hook -> void $ forkIO $ hook t)
+			. M.lookup (transferKey t)
+			. transferHook <$> getDaemonStatus
+
 		finished <- asIO2 finishedTransfer
 		void $ liftIO $ forkIO $ do
 			{- XXX race workaround delay. The location