remote-curl: show progress for fetches over dumb HTTP

remote-curl: show progress for fetches over dumb HTTP

Fetching over dumb HTTP transport doesn't show any progress, even with
the option --progress.  If the connection is slow or there is a lot of
data to get then this can take a long time while the user is left to
wonder if git got stuck.

We don't know the number of objects to fetch at the outset, but we can
count the ones we got.  Show an open-ended progress indicator based on
that number if the user asked for it.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>