Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

mdoc: drop redundant .Pp and .LP calls

They have no effect when coming in pairs, or before .Bl/.Bd

mdoc(7) police: scheduled sweep.

Approved by: re

Minor typo fixes.

Use .Ed to terminate .Bd display.

Deprecate the use of sendmail_enable="NONE" as it adversely affects the
new rcNG effort.

Submitted by: Mike Makonnen <makonnen@pacbell.net>

Add a warning regarding localhost-only listening daemons inside jails.
Apparently binding only to 127.0.0.1 inside of a jail actually binds
to the jail IP address as well (in effect, bind to all available
interfaces in the jail).

Submitted by: Helge Oldach <test-smtp@oldach.net>
MFC after: 1 day
pending RE approval

Quoting Peter Wemm, "At great personal risk, touch the sendmail startup
again."

As an alternative to sendmail_enable=NONE, solve the boot time problem
for non-sendmail users completely by moving all of the sendmail startup
code from /etc/rc to /etc/rc.sendmail. The source for that script will
be kept in src/etc/sendmail/rc.sendmail so make.conf's NO_SENDMAIL will
prevent it from being installed. A new rc.conf variable,
mta_start_script specifies the script to run to start the user's
preferred MTA. For backward compatibility, it will default to
/etc/rc.sendmail. The specified script is called out of /etc/rc after
checking to make sure it exists. A new rc.sendmail.8 man page has also
been added which now houses the sendmail_* variable descriptions
formerly in rc.conf.5.

Use /etc/rc.sendmail in /etc/mail/Makefile to reduce code duplication.

Reviewed by: -current, -stable, obrien, peter, ru
MFC after: 1 week