I noticed format-patch loses authorship information of Lukas' patch
when I run git tools with LC_LANG set to ja_JP.  It turns out that
the sed script to set environment variables were not working on his
name (encoded in UTF-8), which is unfortunate but technically correct.

Force sed invocation under C locale because we always want literal byte
semantics.

Signed-off-by: Junio C Hamano <junkio@cox.net>