convert to withCreateProcess for async exception safety

This handles all sites where checkSuccessProcess/ignoreFailureProcess
is used, except for one: Git.Command.pipeReadLazy
That one will be significantly more work to convert to bracketing.

(Also skipped Command.Assistant.autoStart, but it does not need to
shut down the processes it started on exception because they are
git-annex assistant daemons..)

forceSuccessProcess is done, except for createProcessSuccess.
All call sites of createProcessSuccess will need to be converted
to bracketing.

(process pools still todo also)

Git/Fsck.hs

@@ -77,27 +77,31 @@ findBroken batchmode r = do
 		then toBatchCommand (command, params)
 		else return (command, params)
 	
-	p@(_, _, _, pid) <- createProcess $
-		(proc command' (toCommand params'))
-			{ std_out = CreatePipe
-			, std_err = CreatePipe
-			}
-	(o1, o2) <- concurrently
-		(parseFsckOutput maxobjs r (stdoutHandle p))
-		(parseFsckOutput maxobjs r (stderrHandle p))
-	fsckok <- checkSuccessProcess pid
-	case mappend o1 o2 of
-		FsckOutput badobjs truncated
-			| S.null badobjs && not fsckok -> return FsckFailed
-			| otherwise -> return $ FsckFoundMissing badobjs truncated
-		NoFsckOutput
-			| not fsckok -> return FsckFailed
-			| otherwise -> return noproblem
-		-- If all fsck output was duplicateEntries warnings,
-		-- the repository is not broken, it just has some unusual
-		-- tree objects in it. So ignore nonzero exit status.
-		AllDuplicateEntriesWarning -> return noproblem
+	let p = (proc command' (toCommand params'))
+		{ std_out = CreatePipe
+		, std_err = CreatePipe
+		}
+	withCreateProcess p go
   where
+	go _ (Just outh) (Just errh) pid = do
+		(o1, o2) <- concurrently
+			(parseFsckOutput maxobjs r outh)
+			(parseFsckOutput maxobjs r errh)
+		fsckok <- checkSuccessProcess pid
+		case mappend o1 o2 of
+			FsckOutput badobjs truncated
+				| S.null badobjs && not fsckok -> return FsckFailed
+				| otherwise -> return $ FsckFoundMissing badobjs truncated
+			NoFsckOutput
+				| not fsckok -> return FsckFailed
+				| otherwise -> return noproblem
+			-- If all fsck output was duplicateEntries warnings,
+			-- the repository is not broken, it just has some
+			-- unusual tree objects in it. So ignore nonzero
+			-- exit status.
+			AllDuplicateEntriesWarning -> return noproblem
+	go _ _ _ _ = error "internal"
+	
 	maxobjs = 10000
 	noproblem = FsckFoundMissing S.empty False