The Login page now includes a form to request a password reminder

The Login page now includes a form to request a password reminder
email.  This implies a new server command 'reminder' to do the
sending, which in turn takes advantage of a new sendmail_subprocess()
to send the mail without wedging the server.

There is also a new configuration command reminder_interval, used to
limit the rate at which reminders can be sent to any one user.