--discard-changes is a better name than --force for this option since
it's what really happens. --force is turned to an alias for
--discard-changes. But it's meant to be an alias for potentially more
force options in the future.
Side note. It's not obvious from the patch but --discard-changes also
affects submodules if --recurse-submodules is used. The knob to force
updating submodules is hidden behind unpack-trees.c
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>