revert parentDir change

Reverts 965e106f24

Unfortunately, this caused breakage on Windows, and possibly elsewhere,
because parentDir and takeDirectory do not behave the same when there is a
trailing directory separator.

Build/DistributionUpdate.hs

@@ -64,7 +64,7 @@ getbuild repodir (url, f) = do
 	let dest = repodir </> f
 	let tmp = dest ++ ".tmp"
 	nukeFile tmp
-	createDirectoryIfMissing True (takeDirectory dest)
+	createDirectoryIfMissing True (parentDir dest)
 	let oops s = do
 		nukeFile tmp
 		putStrLn $ "*** " ++ s