switch from System.Cmd.Utils to System.Process

Test suite now passes with -threaded!

I traced back all the hangs with -threaded to System.Cmd.Utils. It seems
it's just crappy/unsafe/outdated, and should not be used. System.Process
seems to be the cool new thing, so converted all the code to use it
instead.

In the process, --debug stopped printing commands it runs. I may try to
bring that back later.

Note that even SafeSystem was switched to use System.Process. Since that
was a modified version of code from System.Cmd.Utils, it needed to be
converted too. I also got rid of nearly all calls to forkProcess,
and all calls to executeFile, which I'm also doubtful about working
well with -threaded.

Git/Queue.hs

@@ -19,7 +19,7 @@ module Git.Queue (
 
 import qualified Data.Map as M
 import System.IO
-import System.Cmd.Utils
+import System.Process
 import Data.String.Utils
 
 import Utility.SafeCommand
@@ -148,11 +148,14 @@ runAction :: Repo -> Action -> IO ()
 runAction repo (UpdateIndexAction streamers) =
 	-- list is stored in reverse order
 	Git.UpdateIndex.streamUpdateIndex repo $ reverse streamers
-runAction repo action@(CommandAction {}) =
-	pOpen WriteToPipe "xargs" ("-0":"git":params) feedxargs
+runAction repo action@(CommandAction {}) = do
+	(Just h, _, _, pid) <- createProcess (proc "xargs" params)
+		{ std_in = CreatePipe }
+	fileEncoding h
+	hPutStr h $ join "\0" $ getFiles action
+	hClose h
+	forceSuccessProcess pid "xargs" params
 	where
-		params = toCommand $ gitCommandLine
+		params = "-0":"git":baseparams
+		baseparams = toCommand $ gitCommandLine
 			(Param (getSubcommand action):getParams action) repo
-		feedxargs h = do
-			fileEncoding h
-			hPutStr h $ join "\0" $ getFiles action