grep: unset GREP_OPTIONS before spawning external grep While we're at it, also unset GREP_COLOR and GREP_COLORS in case colouring is not enabled, to be on the safe side. The presence of these variables alone is not sufficient to trigger coloured output with GNU grep, but other implementations may behave differently. Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx> Signed-off-by: Junio C Hamano <gitster@pobox.com>