more zombie fighting

I'm down to 9 places in the code that can produce unwaited for zombies.

Most of these are pretty innocuous, at least for now, are only
used in short-running commands, or commands that run a set of
actions and explicitly reap zombies after each one.

The one from Annex.Branch.files could be trouble later,
since both Command.Fsck and Command.Unused can trigger it,
and the assistant will be doing those eventally. Ditto the one in
Git.LsTree.lsTree, which Command.Unused uses.

The only ones currently affecting the assistant though, are
in Git.LsFiles. Several threads use several of those.

(And yeah, using pipes or ResourceT would be a less ad-hoc approach,
but I don't really feel like ripping my entire code base apart right
now to change a foundation monad. Maybe one of these days..)

Git/UpdateIndex.hs

@@ -48,7 +48,10 @@ streamUpdateIndex repo as = pipeWrite params repo $ \h -> do
 {- A streamer that adds the current tree for a ref. Useful for eg, copying
  - and modifying branches. -}
 lsTree :: Ref -> Repo -> Streamer
-lsTree (Ref x) repo streamer = mapM_ streamer =<< pipeNullSplit params repo
+lsTree (Ref x) repo streamer = do
+	(s, cleanup) <- pipeNullSplit params repo
+	mapM_ streamer s
+	void $ cleanup
 	where
 		params = map Param ["ls-tree", "-z", "-r", "--full-tree", x]