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.

Command/Vicfg.hs

@@ -39,7 +39,7 @@ seek = withNothing start
 start :: CommandStart
 start = do
 	f <- fromRepo gitAnnexTmpCfgFile
-	createAnnexDirectory $ parentDir f
+	createAnnexDirectory $ takeDirectory f
 	cfg <- getCfg
 	descs <- uuidDescriptions
 	liftIO $ writeFileAnyEncoding f $ genCfg cfg descs