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

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

MFC r239150: nftw(): Do not check the maxfds argument against OPEN_MAX.

Apart from the fact that nothing should have OPEN_MAX as a limit (as opposed
to RLIMIT_NOFILE from getrlimit() or _SC_OPEN_MAX from sysconf()), POSIX
does not require us to check this.

PR: 95239
Submitted by: Todd Miller

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

Approved by: re (implicit)

Replace the current implementations of ftw() and nftw() with the OpenBSD
implementations written by Todd C. Miller. These are cleaner, less buggy
and actively maintained.