Based on v1.7.1.1~23^2 (merge: --log appends shortlog to message if
specified, 2010-05-11). Without this change, the scripted
(non-builtin) merge does not pass t7604.
Cc: Tay Ray Chuan <rctay89@gmail.com> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>