When re-execing git-annex, use current program location, rather than ~/.config/git-annex/program, when possible.

Most of the time, there will be no discreprancy between programPath and
readProgramFile.

But, the programFile might have been written by an old version of git-annex
that is still installed, while a newer one is currently running. In this
case, we want to run the same one that's currently running.

This is especially important for things like the GIT_SSH=git-annex used for
ssh connection caching.

The only code that still uses readProgramFile directly is the upgrade code,
which needs to know where the standalone git-annex was installed, in order to
upgrade it.

Assistant/Threads/Cronner.hs

@@ -15,7 +15,7 @@ import Assistant.Common
 import Assistant.DaemonStatus
 import Utility.NotificationBroadcaster
 import Annex.UUID
-import Config.Files
+import Annex.Path
 import Logs.Schedule
 import Utility.Scheduled
 import Types.ScheduledActivity
@@ -181,7 +181,7 @@ runActivity urlrenderer activity nowt = do
 
 runActivity' :: UrlRenderer -> ScheduledActivity -> Assistant ()
 runActivity' urlrenderer (ScheduledSelfFsck _ d) = do
-	program <- liftIO $ readProgramFile
+	program <- liftIO programPath
 	g <- liftAnnex gitRepo
 	fsckresults <- showFscking urlrenderer Nothing $ tryNonAsync $ do
 		void $ batchCommand program (Param "fsck" : annexFsckParams d)
@@ -196,7 +196,7 @@ runActivity' urlrenderer (ScheduledRemoteFsck u s d) = dispatch =<< liftAnnex (r
 	dispatch Nothing = debug ["skipping remote fsck of uuid without a configured remote", fromUUID u, fromSchedule s]
 	dispatch (Just rmt) = void $ case Remote.remoteFsck rmt of
 		Nothing -> go rmt $ do
-			program <- readProgramFile
+			program <- programPath
 			void $ batchCommand program $ 
 				[ Param "fsck"
 				-- avoid downloading files