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 r245700,245701,245702,245706,245707,245758,245759,245760,245792,245796,
245980,246013:

Automated installation support for bsdinstall.

MFC r226083:
Work around some behavior of gpart that I absolutely do not understand in
order to make every operation of the partition editor fully revertable.
Under *no circumstances* will it any longer touch the disks until the user
presses Finish and confirms it.

Approved by: re (kib)

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

Approved by: re (implicit)

Allow setting of parameters for file systems (e.g. softupdates), turn on
SUJ by default, and allow creation and mounting of FAT filesystems from
the installer.

Import bsdinstall. This is meant to be (eventually in conjunction with
pc-sysinstall) a replacement for sysinstall in the 9.0 release and beyond.
Currently supported platforms are sparc64, pc98, i386, amd64, powerpc, and
powerpc64. Integration into the build system will occur in the coming
weeks.

Merging with pc-sysinstall will use this code as a frontend, while
temporarily retaining the interactive partition editor here. This work
will be done in parallel with improvements on this code and release
integration.

Thanks to all who have provided testing and comments!