Under normal circumstances, and like other git commands,
git checkout will write progress info to stderr if
attached to a terminal. This option allows progress
to be forced even if not using a terminal. Also,
progress can be skipped if using option --no-progress.
Signed-off-by: Edmundo Carmona Antoranz <eantoranz@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>