receive-pack: Wrap status reports inside side-band-64k

receive-pack: Wrap status reports inside side-band-64k

If the client requests the side-band-64k protocol capability we
now wrap the status report data inside of packets sent to band #1.
This permits us to later send additional progress or informational
messages down band #2.

If side-band-64k was enabled, we always send a final flush packet
to let the client know we are done transmitting.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>