t / t5100 / info0011on commit sha1_name.c: teach get_short_sha1() a commit-only option (aa1dec9)
   1Author: A U Thor
   2Email: a.u.thor@example.com
   3Subject: Xyzzy
   4Date: Fri, 8 Aug 2008 13:08:37 +0200 (CEST)
   5