made parentDir return a Maybe FilePath; removed most uses of it

parentDir is less safe than takeDirectory, especially when working
with relative FilePaths. It's really only useful in loops that
want to terminate at /

This commit was sponsored by Audric SCHILTKNECHT.

Upgrade/V1.hs

@@ -73,7 +73,7 @@ moveContent = do
   where
 	move f = do
 		let k = fileKey1 (takeFileName f)
-		let d = parentDir f
+		let d = takeDirectory f
 		liftIO $ allowWrite d
 		liftIO $ allowWrite f
 		moveAnnex k f
@@ -114,7 +114,7 @@ moveLocationLogs = do
 		dest <- fromRepo $ logFile2 k
 		dir <- fromRepo Upgrade.V2.gitStateDir
 		let f = dir </> l
-		liftIO $ createDirectoryIfMissing True (parentDir dest)
+		liftIO $ createDirectoryIfMissing True (takeDirectory dest)
 		-- could just git mv, but this way deals with
 		-- log files that are not checked into git,
 		-- as well as merging with already upgraded