update proxied exporttree=yes remote on receive of sync branch

Since git-annex sync sends the sync branch first, and only displays the
output of the push to the sync branch, this makes git-annex
post-retrieve's output when updating the exported tree be visible when
syncing.

This also makes syncing with a non-bare repository still update the
exported tree, even when the checked out branch is not able to be
updated. The sync branch gets sent regardless.

Command/PostReceive.hs

@@ -22,6 +22,7 @@ import Git.Types
 import Git.Sha
 import qualified Git.Ref
 import Command.Export (filterExport, getExportCommit, seekExport)
+import Command.Sync (syncBranch)
 
 import qualified Data.Set as S
 import qualified Data.ByteString as B
@@ -59,7 +60,8 @@ proxyExportTree = do
 		pushedbranches <- liftIO $ 
 			S.fromList . map snd . parseHookInput
 				<$> B.hGetContents stdin
-		let waspushed = flip S.member pushedbranches
+		let waspushed b = S.member b pushedbranches
+			|| S.member (syncBranch b) pushedbranches
 		case filter (waspushed . Git.Ref.branchRef . fst . snd) rbs of
 			[] -> return ()
 			rbs' -> forM_ rbs' $ \((r, b), _) -> go r b

Command/Sync.hs

@@ -28,6 +28,7 @@ module Command.Sync (
 	parseUnrelatedHistoriesOption,
 	SyncOptions(..),
 	OperationMode(..),
+	syncBranch,
 ) where
 
 import Command

doc/todo/git-annex_proxies.mdwn

@@ -33,9 +33,6 @@ Planned schedule of work:
 * Working on `exportreeplus` branch which is groundwork for proxying to
   exporttree=yes special remotes. Need to merge it to master.
 
-* `git-annex sync` hides output of git-annex post-retreive, which is a
-  problem when it's doing things that are expensive.
-
 * Handle cases where a single key is used by multiple files in the exported
   tree. Need to download from the special remote in order to export
   multiple copies to it. (In particular, this is needed when using