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.

Assistant/WebApp/Configurators/Local.hs

@@ -83,7 +83,7 @@ checkRepositoryPath p = do
 	home <- myHomeDir
 	let basepath = expandTilde home $ T.unpack p
 	path <- absPath basepath
-	let parent = parentDir path
+	let parent = takeDirectory path
 	problems <- catMaybes <$> mapM runcheck
 		[ (return $ path == "/", "Enter the full path to use for the repository.")
 		, (return $ all isSpace basepath, "A blank path? Seems unlikely.")
@@ -416,7 +416,7 @@ startFullAssistant path repogroup setup = do
 canWrite :: FilePath -> IO Bool		
 canWrite dir = do
 	tocheck <- ifM (doesDirectoryExist dir)
-		(return dir, return $ parentDir dir)
+		(return dir, return $ takeDirectory dir)
 	catchBoolIO $ fileAccess tocheck False True False
 
 {- Gets the UUID of the git repo at a location, which may not exist, or