enhance clone and fetch -k experience

enhance clone and fetch -k experience

Now that index-pack can be streamed with a pack, it is probably a good
idea to use it directly instead of creating a temporary file and running
index-pack afterwards.  This way index-pack can abort early whenever a
corruption is encountered even if the pack has not been fully
downloaded, it can display a progress percentage as it knows how much to
expects, and it is a bit faster since the pack indexing is partially
done as data is received. Using fetch -k doesn't need to disable thin
pack generation on the remote end either.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>