t / t4101 / diff.1-3on commit refs.c: refer to "object ID", not "sha1", in error messages (c0bdd65)
   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