Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

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

Hiten's patchset for section four manpages, slightly edited by me.

Uniformly refer to a file system as "file system".

Approved by: re

More file system > filesystem

Removed whitespace at end-of-line; no content changes. I simply did
cd src/share; find man[1-9] -type f|xargs perl -pi -e 's/[ \t]+$//'

BTW, what editors are the culprits? I'm using vim and it shows
me whitespace at EOL in troff files with a thick blue block...

Reviewed by: Silence from cvs diff -b
MFC after: 7 days

mdoc(7) police: use the new features of the Nm macro.

Describe the syncer(4)-related sysctls kern.filedelay, kern.dirdelay
and kern.metadelay, thanks to mckusick's feedback.

Fix a typo and mark ``update'' up consistently in the HISTORY section.

Reported by: des

Include a comment explaining the usual delay between writes and syncs.

Remove mention of SYNCER_MAXDELAY and "thirty seconds", using more
general terms instead. This follows a discussion with alfred,
in which it became clear that I had misunderstood sched_sync().

Replace the obsolete update(4) manual page with syncer(4). I was
not abble to solicit review from <freebsd-hackers>.