Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Remove support for autoloading ACPI from the loader. Leave in the code to
detect ACPI and export info such as the location of the RSDP via hints as
that is still useful.

Set magic fbsd:nokeywords property that allows files to bypass
keyword expansion. (file-specific replacement for CVSROOT/exclude)

Add an 'smap' command that dumps out the BIOS SMAP.

MFC after: 1 week

Remove the last vestiges of the userconfig option. None of this actually
did anything, so this commit should be considered a NO-OP.

Document boot_cdrom, boot_multicons, and boot_serial.
Reduce diffs between help.common and loader(8).
Mention that boot_userconfig is currently a no-op.

s/hint.acpi.0.disable/hint.acpi.0.disabled/

Fix device hints entry for disabling acpi(4).
This also should fix the arbitration with apm(4) when both drivers
are enabled.

Note that your /boot/device.hints needs to be updated if you want to
stop auto-loading acpi.ko or disable acpi(4).

Add help about hint.acpi.0.disable.

Mention that the ACPI module load can be disabled by unsetting $acpi_load

Document root_disk_unit

Reformat help to improve subtopic display appearance, other minor
cleaning. The 'help' command in the loader should now be usable and
hopefully informative.

Build the composite help file from the generic and architecture-specific
help files, sorting topics and subtopics to allow maximum flexibility.

- Add a new command 'lsdev' to list devices which might be likely to host
filesystems.
- New 'help' command and data in the help.* files (not yet installed),
provides topic and subtopic help, indexes, etc.
- Don't crash if the user tries to set an invalid console. Be helpful
instead.
- Expand tabs (badly) on the i386 video console.
- Some minor cosmetic changes.