Since a79ec62 (git-am: Add --ignore-date option, 2009-01-24), git-am.sh
supported the --ignore-date option, and would use the current timestamp
instead of the one provided in the patch if the option was set.
Re-implement this option in builtin/am.c.
Signed-off-by: Paul Tan <pyokagan@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>