The options added to __git_merge_options are those that git-pull passes
to git-merge, since that variable is used by both commands.
Those added directly in _git_merge() are specific to git-merge and
are not passed thru from git-pull.
Reported-by: Haralan Dobrev <hkdobrev@gmail.com>
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>