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/LsTree.hs

@@ -30,7 +30,7 @@ data TreeItem = TreeItem
 {- Lists the contents of a Ref -}
 lsTree :: Ref -> Repo -> IO [TreeItem]
 lsTree t repo = map parseLsTree <$>
-	pipeNullSplit [Params "ls-tree --full-tree -z -r --", File $ show t] repo
+	pipeNullSplitZombie [Params "ls-tree --full-tree -z -r --", File $ show t] repo
 
 {- Parses a line of ls-tree output.
  - (The --long format is not currently supported.) -}