avoid git syncing with instantiate proxied remotes

These remotes have no url configured, so git pull and push will fail.
git-annex sync --content etc can still sync with them otherwise.

Also, avoid git syncing twice with the same url. This is for cases where
a proxied remote has been manually configured and so does have a url.
Or perhaps proxied remotes will get configured like that automatically
later.

Command/Sync.hs

@@ -268,7 +268,8 @@ seek' o = startConcurrency transferStages $ do
 	remotes <- syncRemotes (syncWith o)
 	warnSyncContentTransition o remotes
 	-- Remotes that git can push to and pull from.
-	let gitremotes = filter Remote.gitSyncableRemote remotes
+	let gitremotes = nubBy sameGitRepo $ 
+		filter Remote.gitSyncableRemote remotes
 	-- Remotes that contain annex object content.
 	contentremotes <- filter (\r -> Remote.uuid r /= NoUUID)
 		<$> filterM (not <$$> liftIO . getDynamicConfig . remoteAnnexIgnore . Remote.gitconfig) remotes
@@ -1158,3 +1159,7 @@ splitRemoteAnnexTrackingBranchSubdir tb = (branch, subdir)
 	subdir = if S.null p
 		then Nothing
 		else Just (asTopFilePath p)
+
+sameGitRepo :: Remote -> Remote -> Bool
+sameGitRepo x y = 
+	remoteUrl (Remote.gitconfig x) == remoteUrl (Remote.gitconfig y)

Remote.hs

@@ -451,7 +451,8 @@ claimingUrl' remotefilter url = do
  - with an annex:: url configured? -}
 gitSyncableRemote :: Remote -> Bool
 gitSyncableRemote r
-	| gitSyncableRemoteType (remotetype r) = True
+	| gitSyncableRemoteType (remotetype r) 
+		&& isJust (remoteUrl (gitconfig r)) = True
 	| otherwise = case remoteUrl (gitconfig r) of
 		Just u | "annex::" `isPrefixOf` u -> True
 		_ -> False

doc/todo/git-annex_proxies.mdwn

@@ -44,11 +44,6 @@ For June's work on [[design/passthrough_proxy]], implementation plan:
 * Consider getting instantiated remotes into git remote list.
   See design.
 
-* Make commands like `git-annex sync` not git push/pull to proxied remotes.
-  That doesn't work because they have no url. Or, if proxied remotes are in
-  git remote list, it is unncessary work because it's the same url as the
-  proxy.
-
 * Implement single upload with fanout to proxied remotes.
 
 * Implement clusters.