proxying to exporttree=yes annexobjects=yes basically working

It works when using git-annex sync/push/assist, or when manually sending
all content to the proxied remote before pushing to the proxy remote.
But when the push comes before the content is sent, sending content does
not update the exported tree.

Config.hs

@@ -26,8 +26,12 @@ import Types.Availability
 import Types.GitConfig
 import Types.RemoteConfig
 import Git.Types
+import Git.FilePath
 import Annex.SpecialRemote.Config
 
+import Data.Char
+import qualified Data.ByteString as S
+
 {- Looks up a setting in git config. This is not as efficient as using the
  - GitConfig type. -}
 getConfig :: ConfigKey -> ConfigValue -> Annex ConfigValue
@@ -99,3 +103,12 @@ pidLockFile = ifM (annexPidLock <$> Annex.getGitConfig)
 #else
 pidLockFile = pure Nothing
 #endif
+
+splitRemoteAnnexTrackingBranchSubdir :: Git.Ref -> (Git.Ref, Maybe TopFilePath)
+splitRemoteAnnexTrackingBranchSubdir tb = (branch, subdir)
+  where
+	(b, p) = separate' (== (fromIntegral (ord ':'))) (Git.fromRef' tb)
+	branch = Git.Ref b
+	subdir = if S.null p
+		then Nothing
+		else Just (asTopFilePath p)