Merge branch 'kw/rebase-progress' into next

Merge branch 'kw/rebase-progress' into next

"git rebase", especially when it is run by mistake and ends up
trying to replay many changes, spent long time in silence.  The
command has been taught to show progress report when it spends
long time preparing these many changes to replay (which would give
the user a chance to abort with ^C).

* kw/rebase-progress:
  rebase: turn on progress option by default for format-patch
  format-patch: have progress option while generating patches