update the NULL definition for C++11.  OK deraadt@ guenther@ kettenis@

Based on a diff from Anthony Coulter.
OK krw, halex

OK tb

to /dev/audio*. No port is using them (thanks to sthen@ for checking).
ok sthen@

while here, remove the comment for man6, according to ingo's system...

we don't end up with cryptic error messages.
Regex help from rpe@
Issue reported by Anthony Coulter in rcctl(8), but better fix the root cause.
Also clarify the mage page that rc.d script name must follow ksh(1) variable
naming.
ok robert@ sthen@

before descending, after ascending, but not around single-subdir dirs

While here, also remove two forgotten descriptions for long obsolete
devices.

ok phessler

the SHA512/256 functions as well.

ok jmc naddy

with different magic numbers, so we need to add some functions instead
of just asking the user to truncate as desired. Sigh.
SHA512 is quite a bit faster than SHA256 on 64 bit CPUs,
but 256 bit hashes are usually quite sufficient. Best of both.
ok deraadt tom

from Jacob Berkman, ok beck@

OK many

shortly when we use the hardware thread register in userland

Discussed with and loved by many.
OK tedu@, tom@, deraadt@.

part of the original ISC license that we use in OpenBSD.  Done for
files were Henning is the original author.
OK henning@ deraadt@

ok deraadt@ yasuoka@ reyk@

ok beck

tested by many (thanks!) ok tedu, guenther@

ok krw@ millert@

ok jca@ krw@

as readlink() will tell you that more cheaply.
ok millert@

ok deraadt@

ok deraadt@

ok deraadt@

ok deraadt@

functions out the way of the main body;
ok guenther