It's similar to the default, except that the other windows are hidden.
This ensures that removed/added colors are still visible on the main
merge window, but the other windows not visible.

Specially useful with merge.conflictstyle=diff3.
Signed-off-by: NFelipe Contreras <felipe.contreras@gmail.com>
Acked-by: NDavid Aguilar <davvid@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>