Add 'status_str' to diffinfo output, which stores status (also for
merge commit) as a string. This allows for easy checking if there is
given status among all for merge commit, e.g.
$diffinfo->{'status_str'} =~ /D/;
Signed-off-by: Jakub Narebski <jnareb@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>