t / t4101 / diff.2-0on commit refs.c: refer to "object ID", not "sha1", in error messages (c0bdd65)
   1--- a/frotz
   2+++ b/frotz
   3@@ -1,2 +1,2 @@
   4 a
   5-b
   6\ No newline at end of file
   7+b