Some recent optimizations have been added to pack-objects to reduce
memory usage and some code paths are split into two: one for common
use cases and one for rare ones. Make sure the rare cases are tested
with Travis since it requires manual test configuration that is
unlikely to be done by developers.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>