revision: clear the topo-walk flags in reset_revision_walk

Not doing so can lead to wrong topo-walks when using the revision walk API
consecutively.

Signed-off-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/revision.c b/revision.c
index 0741229..4827360 100644
--- a/revision.c
+++ b/revision.c
@@ -3088,7 +3088,7 @@
 
 void reset_revision_walk(void)
 {
-	clear_object_flags(SEEN | ADDED | SHOWN);
+	clear_object_flags(SEEN | ADDED | SHOWN | TOPO_WALK_EXPLORED | TOPO_WALK_INDEGREE);
 }
 
 static int mark_uninteresting(const struct object_id *oid,