convert to withCreateProcess for async exception safety

Not yet 100% done, so far I've grepped for waitForProcess and converted
everything that uses that to start the process with withCreateProcess.

Except for some things like P2P.IO and Assistant.TransferrerPool,
and Utility.CoProcess, that manage a pool of processes. See #2
in https://git-annex.branchable.com/todo/more_extensive_retries_to_mask_transient_failures/#comment-209f8a8c38e63fb3a704e1282cb269c7
for how those will need to be dealt with.

checkSuccessProcess, ignoreFailureProcess, and forceSuccessProcess calls waitForProcess, so
callers of them will also need to be dealt with, and have not been yet.

Git/History.hs

@@ -50,19 +50,22 @@ data HistoryCommit = HistoryCommit
 {- Gets a History starting with the provided commit, and down to the
  - requested depth. -}
 getHistoryToDepth :: Integer -> Ref -> Repo -> IO (Maybe (History HistoryCommit))
-getHistoryToDepth n commit r = do
-	(_, Just inh, _, pid) <- createProcess (gitCreateProcess params r)
-		{ std_out = CreatePipe }
-	!h <- fmap (truncateHistoryToDepth n) 
-		. build Nothing 
-		. map parsehistorycommit
-		. map L.toStrict
-		. L8.lines
-		<$> L.hGetContents inh
-	hClose inh
-	void $ waitForProcess pid
-	return h
+getHistoryToDepth n commit r = withCreateProcess p go
   where
+	p = (gitCreateProcess params r)
+		{ std_out = CreatePipe }
+	go _ (Just inh) _ pid = do
+		!h <- fmap (truncateHistoryToDepth n) 
+			. build Nothing 
+			. map parsehistorycommit
+			. map L.toStrict
+			. L8.lines
+			<$> L.hGetContents inh
+		hClose inh
+		void $ waitForProcess pid
+		return h
+	go _ _ _ _ = error "internal"
+
 	build h [] = fmap (mapHistory fst) h
 	build _ (Nothing:_) = Nothing
 	build Nothing (Just v:rest) =