Expand checkurl to support recommended filename, and multi-file-urls

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Remote/GCrypt.hs

@@ -123,7 +123,7 @@ gen' r u c gc = do
 		, mkUnavailable = return Nothing
 		, getInfo = return $ gitRepoInfo r
 		, claimUrl = Nothing
-		, checkUrl = const $ return Nothing
+		, checkUrl = Nothing
 	}
 	return $ Just $ specialRemote' specialcfg c
 		(simplyPrepare $ store this rsyncopts)