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)

Add several necessary .El's.

MFC after: 2 weeks

Add manpages for BUF_RECURSED(9) and BUF_ISLOCKED(9) and connect them to
the build.

Reviewed by: brueffer