t / t4101 / diff.3-1on commit builtin/show-ref: rewrite to take an object_id argument (6c4461e)
   1--- a/frotz
   2+++ b/frotz
   3@@ -1,3 +1,3 @@
   4 a
   5+b
   6 c
   7-b
   8\ No newline at end of file