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)

mdoc: order prologue macros consistently by Dd/Dt/Os

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by: ru
Approved by: philip, ed (mentors)

Correct the HISTORY section of these man pages to show when the function,
not the "manual page example" was introduced.

Approved by: ed (mentor, implicit)
MFC after: 1 week

Remove duplicate (but commented out) .Sh HISTORY section heading.
It almost "shadows" the ending .El request of a list, which seems
to have caused mdoc buglets in some gss_*.3 manpages.

MFC after: 3 days

Move the Internet Society copyright message so that it appears in the
formatted page as well as the source.

Add a new extensible GSS-API layer which can support GSS-API plugins,
similar the the Solaris implementation. Repackage the krb5 GSS mechanism
as a plugin library for the new implementation. This also includes a
comprehensive set of manpages for the GSS-API functions with text mostly
taken from the RFC.

Reviewed by: Love Hörnquist Åstrand <lha@it.su.se>, ru (build system), des (openssh parts)