we could save a little bit of memory when buffering in a later mode
by just passing the inner part ("%s and %s", file1, file 2), but
those a just a few bytes, so instead let's reuse the implementation from
DIFF_SYMBOL_HEADER and keep the whole line around.
Signed-off-by: NStefan Beller <sbeller@google.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>