Fix use of several config settings

annex.ssh-options, annex.rsync-options, annex.bup-split-options.

And adjust types to avoid the bugs that broke several config settings
recently. Now "annex." prefixing is enforced at the type level.

Backend.hs

@@ -46,7 +46,7 @@ orderedList = do
 			l' <- (lookupBackendName name :) <$> standard
 			Annex.changeState $ \s -> s { Annex.backends = l' }
 			return l'
-		standard = parseBackendList <$> getConfig "annex.backends" ""
+		standard = parseBackendList <$> getConfig (annexConfig "backends") ""
 		parseBackendList [] = list
 		parseBackendList s = map lookupBackendName $ words s