This patch adds support for expiring user passwords.
The following statements are extended:
  CREATE USER user@localhost PASSWORD EXPIRE [option]
  ALTER USER user@localhost PASSWORD EXPIRE [option]
If no option is specified, the password is expired with immediate
effect. If option is DEFAULT, global policy applies according to
the default_password_lifetime system var (if 0, password never
expires, if N, password expires every N days). If option is NEVER,
the password never expires and if option is INTERVAL N DAY, the
password expires every N days.
The feature also supports the disconnect_on_expired_password system
var and the --connect-expired-password client option.

Closes #1166