When the passwd is called on a system with a date set to 1st Jan
1970, the change date is set to 0, which has a special meaning:
"The value 0 has a special meaning, which is that the user should change
her pasword the next time she will log in the system."
Thanks to this patch, when the password is changed on 1st on Jun 1970 the
change date is set to 1.
Signed-off-by: Adam Wujek <firstname.lastname@example.org>