Keep the ZIP central directory, which is written after all archive
entries, in a strbuf instead of a custom-managed buffer. It contains
binary data, so we can't (and don't want to) use the full range of
strbuf functions and we don't need the terminating NUL, but the result
is shorter and simpler code.
Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>