fix sync --content with remote.name.annex-tracking-branch=master:subdir

It was exporting the whole tree not just the subdir. Now tested fully
working in both directions.

Command/Sync.hs

@@ -726,16 +726,13 @@ seekExportContent o rs (currbranch, _) = or <$> forM rs go
 		(exported, mtbcommitsha) <- case remoteAnnexTrackingBranch (Remote.gitconfig r) of
 			Nothing -> nontracking r
 			Just b -> do
+				mtree <- inRepo $ Git.Ref.tree b
 				mtbcommitsha <- Command.Export.getExportCommit r b
-				mcur <- maybe
-					(return Nothing)
-					(inRepo . Git.Ref.tree)
-					(fmap snd mtbcommitsha)
-				case mcur of
-					Nothing -> nontracking r
-					Just cur -> do
-						Command.Export.changeExport r db cur
-						return ([mkExported cur []], mtbcommitsha)
+				case (mtree, mtbcommitsha) of
+					(Just tree, Just _) -> do
+						Command.Export.changeExport r db tree
+						return ([mkExported tree []], mtbcommitsha)
+					_ -> nontracking r
 		fillexport r db (exportedTreeishes exported) mtbcommitsha
 		
 	nontracking r = do

doc/todo/import_tree.mdwn

@@ -10,13 +10,6 @@ this.
 
 ## implementation notes
 
-* Does sync --content with remote.name.annex-tracking-branch=master:subdir
-  export the right tree and update the remote tracking branch right?
-  Does it import correctly?
-
-* Need to support annex-tracking-branch configuration, which documentation
-  says makes git-annex sync and assistant do imports.
-
 * When on an adjusted unlocked branch, need to import the files unlocked.
   Also, the tracking branch code needs to know about such branches,
   currently it will generate the wrong tracking branch.