We use the "buf" strbuf for two things: to read incoming
lines, and as a scratch space for test-expanding the
user-provided format. Let's split this into two variables
with descriptive names, which makes their purpose and
lifetime more clear.
It will also help in a future patch when we start using the
"output" buffer for more expansions.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>