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

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

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

Approved by: re (implicit)

Because ggatel(8) operates on local GEOM providers, use unlimited queue size in
GEOM GATE to fix the issue described in r220264. This also means that we no
longer need -q option, remove it. Don't bother to leaving it as a no-op, as
ggatel(8) is just an example utility.

Sort sections.

Added the EXIT STATUS section where appropriate.

Polish the mdoc(7) markup.

Add missing commands.

GEOM Gate local control utility.