expose Control.Monad.join

I think I've been looking for that function for some time.
Ie, I remember wanting to collapse Just Nothing to Nothing.

Command/AddUrl.hs

@@ -156,7 +156,7 @@ url2file url pathdepth = case pathdepth of
 		| otherwise -> error "bad --pathdepth"
   where
 	fullurl = uriRegName auth ++ uriPath url ++ uriQuery url
-	frombits a = join "/" $ a urlbits
+	frombits a = intercalate "/" $ a urlbits
 	urlbits = map (filesize . escape) $ filter (not . null) $ split "/" fullurl
 	auth = fromMaybe (error $ "bad url " ++ show url) $ uriAuthority url
 	filesize = take 255

Command/InitRemote.hs

@@ -31,7 +31,7 @@ start [] = do
 	error $ "Specify a name for the remote. " ++
 		if null names
 			then ""
-			else "Either a new name, or one of these existing special remotes: " ++ join " " names
+			else "Either a new name, or one of these existing special remotes: " ++ intercalate " " names
 start (name:ws) = do
 	(u, c) <- findByName name
 	let fullconfig = config `M.union` c	

Command/TransferKeys.hs

@@ -95,7 +95,7 @@ runRequests readh writeh a = do
 
 sendRequest :: Transfer -> AssociatedFile -> Handle -> IO ()
 sendRequest t f h = do
-	hPutStr h $ join fieldSep
+	hPutStr h $ intercalate fieldSep
 		[ serialize (transferDirection t)
 		, serialize (transferUUID t)
 		, serialize (transferKey t)

Command/Version.hs

@@ -27,12 +27,10 @@ start = do
 		showPackageVersion
 		putStrLn $ "local repository version: " ++ fromMaybe "unknown" v
 		putStrLn $ "default repository version: " ++ defaultVersion
-		putStrLn $ "supported repository versions: " ++ vs supportedVersions
-		putStrLn $ "upgrade supported from repository versions: " ++ vs upgradableVersions
+		putStrLn $ "supported repository versions: " ++ unwords supportedVersions
+		putStrLn $ "upgrade supported from repository versions: " ++ unwords upgradableVersions
 		putStrLn $ "build flags: " ++ unwords buildFlags
 	stop
-  where
-	vs = join " "
 
 showPackageVersion :: IO ()
 showPackageVersion = putStrLn $ "git-annex version: " ++ SysConfig.packageversion