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.

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)