ok deraadt@, millert@, krw@ - mdoc ok jmc@

This allows an application to only update a password entry if it is
in the state it expects.  Additionally, if the old passwd struct
is specified the new one may have a different pw_name field since
matching is done on the original.  Adapted from FreeBSD.

This allows for safe abort handling, without tripping into
false recursivity problems.
Ok tedu@, deraadt@

instead of 16.  E.g. it is now /dev/{p,t}typ[0-9a-zA-z] instead of just
/dev/{p,t}typ[0-9a-f].  This requires that you update MAKEDEV and run:
# cd /dev && ./MAKEDEV pty0 && rm -f [pt]ty[rq]*

ok deraadt@

from Jon Mosco;

ok miod@ krw@

lets tendra build again.
ok deraadt@, pvalchev@, millert@

ok millert@ deraadt@ jason@

from Daniel Lucq

ok beck@ millert@

Bring carp interfaces down at shutdown, to make a graceful exit if we're master.
ok deraadt@

ok deraadt@

ok deraadt@

ok markus@ henning@

switching to that securelevel, and the clock is off by more than
128ms, ntpd will attempt to correct by stepping the clock instead of
slewing it. So use -x in that case; from tholo

ok marc@ fgsch@

advance. From Thorsten Lockert.

No regen necessary except for hp300 MAKEDEV.8

Allows others to build OpenBSD/cats, use binutils from devel/binutils/stable
Requested by deraadt@