teach send-pack about --[no-]progress

teach send-pack about --[no-]progress

The send_pack function gets a "progress" flag saying "yes,
definitely show progress" or "no, definitely do not show
progress". This gets set properly by transport_push when
send_pack is called directly.

However, when the send-pack command is executed separately
(as it is for the remote-curl helper), there is no way to
tell it "definitely do this". As a result, we do not
properly respect "git push --no-progress" for smart-http
remotes; you will still get progress if stderr is a tty.

This patch teaches send-pack --progress and --no-progress,
and teaches remote-curl to pass the appropriate option to
override send-pack's isatty check. This fixes the
--no-progress case above, and as a bonus, also makes "git
push --progress" work when stderr is not a tty.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>