add git ls-tree --long parser

Not yet used, but allows getting the size of items in the tree fairly
cheaply.

I noticed that CmdLine.Seek uses ls-tree and the feeds the files into
another long-running process to check their size. That would be an
example of a place that might be sped up by using this. Although in that
particular case, it only needs to know the size of unlocked files, not
locked. And since enabling --long probably doubles the ls-tree runtime
or more, the overhead of using it there may outwweigh the benefit.

Command/Info.hs

@@ -589,7 +589,10 @@ getDirStatInfo o dir = do
 getTreeStatInfo :: InfoOptions -> Git.Ref -> Annex (Maybe StatInfo)
 getTreeStatInfo o r = do
 	fast <- Annex.getState Annex.fast
-	(ls, cleanup) <- inRepo $ LsTree.lsTree LsTree.LsTreeRecursive r
+	(ls, cleanup) <- inRepo $ LsTree.lsTree
+		LsTree.LsTreeRecursive
+		(LsTree.LsTreeLong False)
+		r
 	(presentdata, referenceddata, repodata) <- go fast ls initial
 	ifM (liftIO cleanup)
 		( return $ Just $