better name for fallback sync refs

Don't expose these as branches in refs/heads/. Instead hide them away in
refs/synced/ where only show-ref will find them.

Make unused only look at branches and tags, not these other things,
so it won't care if some stale sync ref used to use a file.

This means they don't need to be deleted, which could have
led to an incoming sync being missed.

Assistant/Sync.hs

@@ -90,7 +90,7 @@ pushToRemotes threadname now st mpushmap remotes = do
 	go True branch g u remotes
 	where
 		go _ Nothing _ _ _ = return True -- no branch, so nothing to do
-		go shouldretry (Just branch) g u rs = do
+		go shouldretry (Just branch) g u rs =  do
 			debug threadname
 				[ "pushing to"
 				, show rs
@@ -133,12 +133,12 @@ pushToRemotes threadname now st mpushmap remotes = do
 			, Param $ refspec branch
 			] g
 			where
+				{- Push to refs/synced/uuid/branch; this
+				 - avoids cluttering up the branch display. -}
 				refspec b = concat
 					[ s
 					, ":"
-					, show $ Git.Ref.base $
-						Command.Sync.syncBranch $ Git.Ref $
-							"fallback" </> fromUUID u </> s
+					, "refs" </> "synced" </> fromUUID u </> s
 					]
 					where s = show $ Git.Ref.base b