merge script: --ff-only to disallow true merge Port v1.6.6-rc0~62^2 (Teach 'git merge' and 'git pull' the option --ff-only, 2009-10-29) to the old merge script. Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>