For testing truncated log messages 'commit_msg' function uses `sed` to
cut a message. On various platforms `sed` behaves differently and
results of its work depend on locales installed. So, avoid using `sed`.
Use predefined expected outputs instead of calculated ones.
Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>