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it's just crappy/unsafe/outdated, and should not be used.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

Utility/Lsof.hs

@@ -12,6 +12,7 @@ module Utility.Lsof where
 import Common
 
 import System.Posix.Types
+import System.Process
 
 data LsofOpenMode = OpenReadWrite | OpenReadOnly | OpenWriteOnly | OpenUnknown
 	deriving (Show, Eq)
@@ -34,10 +35,8 @@ queryDir path = query ["+d", path]
  -}
 query :: [String] -> IO [(FilePath, LsofOpenMode, ProcessInfo)]
 query opts = do
-	(pid, s) <- pipeFrom "lsof" ("-F0can" : opts)
-	let !r = parse s
-	void $ getProcessStatus True False $ processID pid
-	return r
+	(_, s, _) <- readProcessWithExitCode "lsof" ("-F0can" : opts) []
+	return $ parse s
 
 {- Parsing null-delimited output like:
  -