Kevin Willford authored Aug 10, 2017 and Junio C Hamano committed Aug 14, 2017

When generating patches for the rebase command, if the user does
not realize the branch they are rebasing onto is thousands of
commits different, there is no progress indication after initial
rewinding message.

The progress meter as presented in this patch assumes the thousands of
patches to have a fine granularity as well as assuming to require all
the same amount of work/time for each, such that a steady progress bar
is achieved.

We do not want to estimate the time for each patch based e.g.
on their size or number of touched files (or parents) as that is too
expensive for just a progress meter.

This patch allows a progress option to be passed to format-patch
so that the user can be informed the progress of generating the
patch.  This option is then used by the rebase command when
calling format-patch.

Signed-off-by: Kevin Willford <kewillf@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>