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)

Style: NO_MAN doesn't need any value.

Add a simple regression test for mlock()/munlock() to make sure they
work on a single page as root, and fails on a single page as nobody.
Intended to help diagnose reports regarding insecure memory use with
gnupg.