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

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

MFC r264841: Update zfsboot to coincide with MFC of r264840
adding GEOM support.

MFC r264488:

When merging docsinstall and zfsboot updates to stable/9 it was discovered
that the slightly older dialog(1) requires --separate-output when using the
--checklist widget to force response to produce unquoted values (whereas in
stable/10 --checklist widget without --separate-output will only quote the
checklist labels in the response if the label is multi-word (contains any
whitespace).

Since these enhancements (see revisions 263956 and 264437) were developed
originally on 10, the --separate-output option was omitted. When merged to
stable/9, we (Allan Jude) and I found during testing that the "always-
quoting" of the response was causing things like struct interpolation to
fail (`f_struct device_$dev' would produce `f_struct device_\"da0\"' for
example -- literal quotes inherited from dialog(1) --checklist response).

To see the behavior, execute the following on stable/9 versus stable/10:

dialog --checklist disks: 0 0 0 da0 "" off da1 "" off

Check both items and hit enter. On stable/10, the response is:

da0 da1

On stable/9 the response is:

"da0" "da1"

If you use the --separate-output option, the response is the same for both:

da0
da1

So applying --separate-output on every platform until either one of two
things occurs 1) dialog(1,3) gets synchronized between stable/9, higher or
2) we drop support for stable/9.

Reviewed by: Allan Jude

MFC r256343,256540-256541,256544,256549,256551,256553,257939,258021,258927,
259144,259148,259470,259472,259474,259476-259478,259480-259481,259570,
259597-259598, and 261960 (24 revisions; summarized below)...
r256343: Add zfsboot module as an option for automatic configuration
r256540: Add zpool_cache_* variables to loader.conf(5)
r256541: Document BSDINSTALL_TMPBOOT in bsdinstall.8
r256544: Fix a typo when setting up loader.conf(5) GELI entries
r256549: Document zfsboot in bsdinstall.8
r256551: Bump .Dd date in bsdinstall.8
r256553: Align ZFSBOOT_BEROOT_NAME with sysutils/beadm + Solaris beadm
r257939: Validate scripted partition entry before acting on disks
r258021: Switch default MBR bootcode from /boot/boot0 to /boot/mbr
r258927: Fix early regression in enabling the Encryption feature
r259144: Fix early regression in entering passphrase for Encryption
r259148: Fix typo that broke booting from Encrypted setup
r259470: Add default /var/mail with atime=on for mail apps
r259472: Accept NULL input as also meaning zero swap
r259474: Bug fixes and debugging improvements
r259476: Improve default ZFS disk layout
r259477: fletcher4 is currently the default
r259478: De-uglify the geli(8)-setup infobox by adding a newline
r259480: Fix ghosted zroot pool issue
r259481: Auto-enable 4k alignment with Encryption
r259570: Fix "[: -eq: argument expected" error
r259597: Fix installation to 3-4+ disks
r259598: Set the cachefile property so bootpools get imported
r261960: Add zfsboot to scripted interface of bsdinstall

Add zfsboot module as an option for automatic configuration. Default is
to run interactively but it can be scripted too (optinally completely
non-interactive). Currently supports GELI and all ZFS vdev types. Also
performs validation on selections/settings providing error messages if
necessary, explaining (in plain language) what the issue is. Currently
the auto partitioning of naked disks only supports GPT and MBR (VTOC8
pending for sparc64), so is only available for i386/amd64 install.

Submitted by: Allan Jude <freebsd@allanjude.com>, myself
Reviewed by: Allan Jude <freebsd@allanjude.com>
Approved by: re (glebius)