bring back default SIGINT handler

This seems to fix a problem I've recently seen where ctrl-c during rsync
leads to `git annex get` moving on to the next thing rather than exiting.

Seems likely that started happening with the switch to System.Process
(d1da9cf221), as the old code took care
to install a default SIGINT handler.

Note that since the bug was only occurring sometimes, I am not 100% sure
I've squashed it, although I seem to have.

CmdLine.hs

@@ -15,6 +15,7 @@ import qualified Control.Exception as E
 import qualified Data.Map as M
 import Control.Exception (throw)
 import System.Console.GetOpt
+import System.Posix.Signals
 
 import Common.Annex
 import qualified Annex
@@ -108,7 +109,9 @@ tryRun' errnum state cmd (a:as) = do
 
 {- Actions to perform each time ran. -}
 startup :: Annex Bool
-startup = return True
+startup = liftIO $ do
+	void $ installHandler sigINT Default Nothing
+	return True
 
 {- Cleanup actions. -}
 shutdown :: Bool -> Annex Bool

Utility/Rsync.hs

@@ -53,7 +53,7 @@ rsync = boolSystem "rsync"
  - The params must enable rsync's --progress mode for this to work.
  -}
 rsyncProgress :: (Integer -> IO ()) -> [CommandParam] -> IO Bool
-rsyncProgress callback params = catchBoolIO $
+rsyncProgress callback params = 
 	withHandle StdoutHandle createProcessSuccess p (feedprogress 0 [])
 	where
 		p = proc "rsync" (toCommand params)

Utility/SafeCommand.hs

@@ -49,8 +49,6 @@ boolSystemEnv command params environ = dispatch <$> safeSystemEnv command params
 safeSystem :: FilePath -> [CommandParam] -> IO ExitCode
 safeSystem command params = safeSystemEnv command params Nothing
 
-{- Unlike many implementations of system, SIGINT(ctrl-c) is allowed
- - to propigate and will terminate the program. -}
 safeSystemEnv :: FilePath -> [CommandParam] -> Maybe [(String, String)] -> IO ExitCode
 safeSystemEnv command params environ = do
 	(_, _, _, pid) <- createProcess (proc command $ toCommand params)

doc/bugs/signal_weirdness.mdwn

@@ -14,7 +14,7 @@ For example:
 Here git-annex exits before rsync has fully exited. Not a large problem
 but sorta weird.
 
-The culprit is `safeSystemEnv` in Utility.SafeCommand, which installs
+The culprit is `CmdLine.startup` in Utility.SafeCommand, which installs
 a default signal handler for SIGINT, which causes it to immediatly
 terminate git-annex. rsync, in turn, has its own SIGINT handler, which 
 prints the message, typically later.