mostly finished with createDirectoryUnder conversion

Remaining things needing converted are in the assistant, and Annex.Ssh.

Every other remaining call to createDirectoryIfMissing True has been
audited and is not relevant. The ones in Build/ of course don't get
included in the program. Others included eg, Remote.Tahoe and
Config.Files which both write to dotfiles under the home directory.

Git/Repair.hs

@@ -245,8 +245,9 @@ explodePackedRefsFile r = do
 		nukeFile f
   where
 	makeref (sha, ref) = do
-		let dest = fromRawFilePath (localGitDir r) </> fromRef ref
-		createDirectoryIfMissing True (parentDir dest)
+		let gitd = fromRawFilePath (localGitDir r)
+		let dest = gitd </> fromRef ref
+		createDirectoryUnder gitd (parentDir dest)
 		unlessM (doesFileExist dest) $
 			writeFile dest (fromRef sha)