bisect_next_all: convert xsnprintf to xstrfmt

bisect_next_all: convert xsnprintf to xstrfmt

Git can't run bisect between 2048+ commits if use russian
translation, because the translated string is too long for the fixed
buffer it uses (this can be reproduced "LANG=ru_RU.UTF8 git bisect
start v4.9 v4.8" on linux sources).

Use xstrfmt() to format the message string to sufficiently sized
buffer instead to fix this.

Signed-off-by: Maxim Moseychuk <franchesko.salias.hudro.pedros@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>