support required groupwanted

When the required content is set to "groupwanted", use whatever expression
has been set in groupwanted as the required content of the repo, similar to
how setting required content to "standard" already worked.

Logs/PreferredContent.hs

@@ -92,8 +92,9 @@ preferredRequiredMapsLoad' mktokens = do
 		in simpleMap
 			. parseLogOldWithUUID (\u -> mk u . decodeBS <$> A.takeByteString)
 			<$> Annex.Branch.get l
-	pc <- genmap preferredContentLog =<< groupPreferredContentMapRaw
-	rc <- genmap requiredContentLog M.empty
+	gm <- groupPreferredContentMapRaw
+	pc <- genmap preferredContentLog gm
+	rc <- genmap requiredContentLog gm
 	-- Required content is implicitly also preferred content, so combine.
 	let pc' = M.unionWith combiner pc rc
 	return (pc', rc)