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 even more redundant .Pp calls

No change in rendered output, less mandoc lint warnings.

Tool provided by: Nobuyuki Koganemaru n-kogane at syd.odn.ne.jp

Add support for backing up the old kernel when installing a new kernel
using freebsd-update. This applies to using freebsd-update in "upgrade
mode" and normal freebsd-update on a security branch.

The backup kernel will be written to /boot/kernel.old, if the directory
does not exist, or the directory was created by freebsd-update in a
previous backup. Otherwise freebsd-update will generate a new directory
name for use by the backup. By default symbol files are not backed up
to save diskspace and avoid filling up the root partition.

This feature is fully configurable in the freebsd-update config file,
but defaults to enabled.

MFC after: 1 week (stable/7)
Reviewed by: cperciva
Approved by: re (kib)

Document new IDSIgnorePaths directive.

Add support for "freebsd-update -r newrelease upgrade" -- binary
upgrading to new releases. Important parts of this code include
* automatically determining which optional components (e.g., src,
info, proflibs) are installed.
* merging changes in files which are modified locally and have
changed between the currently running and new release.
* prompting the user to rebuild all 3rd party software before
deleting old shared libraries.

Yes, this is compatible with "freebsd-update rollback" -- you can
test a new -BETA and roll back to the old release if you don't
like it.

Subject to re@ approval, this will be MFCed before 7.0-BETA3 and
6.3-RC1.

MFC after: 2 days

Revise markup.

Add FreeBSD Update 2.0 client code. The build code is in the projects
repository.

Sponsored by: FreeBSD security development fundraiser