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 r245680:

Make "Finish" the default choice in the partition editor. This lets you
successfully complete an installation with all defaults by pressing
Enter repeatedly until your machine reboots.

MFC r237253:
Remove variables which are initialized but never used thereafter reported by gcc46 warning

Approved by: cperciva (implicit)

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)

Implement support for GRAID volumes in the installer partition editor,
rename a few options, clarify some help text, and add help text for the
buttons on the main partition editor screen.

Approved by: re (kib)

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!