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)

Fix a copy+paste error by checking the correct variable against MM_NULLACT.

PR: 140386
Submitted by: soulcatcher <soulcatcher13@gmail.com
MFC after: 1 week

Back out the `hiding' of strlcpy and strlcat. Several people
vocally objected to this safety belt.

`Hide' strlcpy and strlcat (using the namespace.h / __weak_reference
technique) so that we don't wind up calling into an application's
version if the application defines them.

Inspired by: qpopper's interfering and buggy version of strlcpy

Fix a memory leak.

o Fix a memory leak.
o Rewrite validmsgverb() so that it works (I'm not sure how it escaped
my original testing).
o Document nextcomp().

Implement POSIX.1-2001 (XSI)'s fmtmsg(3).