git-http-fetch: Remove size limit for objects/info/{packs,alternates}

git-http-fetch: Remove size limit for objects/info/{packs,alternates}

git-http-fetch received objects/info/packs into a fixed-size buffer
and started to fail when this file became larger than the buffer.
Change it to grow the buffer dynamically, and do the same thing for
objects/info/alternates.  Also add missing free() calls for these
buffers.

Signed-off-by: Sergey Vlasov <vsu@altlinux.ru>
Signed-off-by: Junio C Hamano <junkio@cox.net>