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 r261522:

Describe the use of a freebsd-boot GPT partition, brought up by Scot
Hetzel <swhetzel@gmail.com> on the -doc mailing list.

Also modify the Author section to be clear that I wrote the man page,
not gptboot.

MFC r245910,r247370,r249371,r252492,r252586:

r252586:

Add descriptions to the FILES list, fix some mdoc complaints, move the
"neither" entry out of the table in BOOTING.

r252492:

Add a new gptboot(8) man page. Factor out the redundant information
in gpart(8) and boot(8), adding references to gptboot(8) in both.

r249371:

Remove kernel options from the SYNOPSIS. They are already documented in the
geom(4) manual page SYNOPSIS.

r247370:

Fix typo in EFI GPT GUID.

r245910:

Expand description of how gptboot and gptzfsboot choose a partition for
booting.

Add a new gptboot(8) man page. Factor out the redundant information
in gpart(8) and boot(8), adding references to gptboot(8) in both.

Reviewed by: jhb, ae, pjd, Paul Schenkeveld <bsdcan@psconsult.nl>, david_a_bright@dell.com (portions), gjb
MFC after: 1 week