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it's just crappy/unsafe/outdated, and should not be used.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.

Command/Map.hs

@@ -9,6 +9,7 @@ module Command.Map where
 
 import Control.Exception.Extensible
 import qualified Data.Map as M
+import System.Process
 
 import Common.Annex
 import Command
@@ -198,9 +199,13 @@ tryScan r
 			case result of
 				Left _ -> return Nothing
 				Right r' -> return $ Just r'
-		pipedconfig cmd params = safely $
-			pOpen ReadFromPipe cmd (toCommand params) $
-				Git.Config.hRead r
+		pipedconfig cmd params = safely $ do
+			(_, Just h, _, pid) <-
+				createProcess (proc cmd $ toCommand params)
+					{ std_out = CreatePipe }
+			r' <- Git.Config.hRead r h
+			forceSuccessProcess pid cmd $ toCommand params
+			return r'
 
 		configlist =
 			onRemote r (pipedconfig, Nothing) "configlist" [] []