add whenM and unlessM

Just more golfing.. I am pretty sure something in a library somewhere can
do this, but I have been unable to find it.

Remote/Bup.hs

@@ -11,7 +11,7 @@ import qualified Data.ByteString.Lazy.Char8 as L
 import IO
 import Control.Exception.Extensible (IOException)
 import qualified Data.Map as M
-import Control.Monad (unless, when)
+import Control.Monad (when)
 import Control.Monad.State (liftIO)
 import System.Process
 import System.Exit
@@ -75,8 +75,7 @@ bupSetup u c = do
 	-- bup init will create the repository.
 	-- (If the repository already exists, bup init again appears safe.)
 	showNote "bup init"
-	ok <- bup "init" buprepo []
-	unless ok $ error "bup init failed"
+	bup "init" buprepo [] <|> error "bup init failed"
 
 	storeBupUUID u buprepo
 
@@ -172,9 +171,9 @@ storeBupUUID u buprepo = do
 	if Git.repoIsUrl r
 		then do
 			showNote "storing uuid"
-			ok <- onBupRemote r boolSystem "git"
+			onBupRemote r boolSystem "git"
 				[Params $ "config annex.uuid " ++ u]
-			unless ok $ do error "ssh failed"
+				<|> error "ssh failed"
 		else liftIO $ do
 			r' <- Git.configRead r
 			let olduuid = Git.configGet r' "annex.uuid" ""

Remote/Directory.hs

@@ -62,8 +62,8 @@ directorySetup u c = do
 	-- verify configuration is sane
 	let dir = maybe (error "Specify directory=") id $
 		M.lookup "directory" c
-	e <- liftIO $ doesDirectoryExist dir
-	when (not e) $ error $ "Directory does not exist: " ++ dir
+	liftIO $ doesDirectoryExist dir
+		<|> error $ "Directory does not exist: " ++ dir
 	c' <- encryptionSetup c
 
 	-- The directory is stored in git config, not in this remote's

Remote/Rsync.hs

@@ -10,7 +10,7 @@ module Remote.Rsync (remote) where
 import qualified Data.ByteString.Lazy.Char8 as L
 import Control.Exception.Extensible (IOException)
 import qualified Data.Map as M
-import Control.Monad.State (liftIO, when)
+import Control.Monad.State (liftIO)
 import System.FilePath
 import System.Directory
 import System.Posix.Files
@@ -168,9 +168,8 @@ withRsyncScratchDir a = do
 	nuke tmp
 	return res
 	where
-		nuke d = liftIO $ do
-			e <- doesDirectoryExist d
-			when e $ liftIO $ removeDirectoryRecursive d
+		nuke d = liftIO $ 
+			doesDirectoryExist d <&> removeDirectoryRecursive d
 
 rsyncRemote :: RsyncOpts -> [CommandParam] -> Annex Bool
 rsyncRemote o params = do