scan reflogs independently from refs

Currently, the search for all reflogs depends on the existence of
corresponding refs under the .git/refs/ directory.  Let's scan the
.git/logs/ directory directly instead.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>
diff --git a/reachable.c b/reachable.c
index a6a3348..01760d7 100644
--- a/reachable.c
+++ b/reachable.c
@@ -188,9 +188,9 @@
 	/* Add all external refs */
 	for_each_ref(add_one_ref, revs);
 
-	/* Add all reflog info from refs */
+	/* Add all reflog info */
 	if (mark_reflog)
-		for_each_ref(add_one_reflog, revs);
+		for_each_reflog(add_one_reflog, revs);
 
 	/*
 	 * Set up the revision walk - this will move all commits