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)

Correct some style nits that I have mistakenly submitted as
suggestions which result in the last revision[*]:
- style(9) and sysexits(3) suggests that we use EX_*
as exit values, instead of some other values like
those returned from a system call as errno.

Additionally, follow Ruslan's suggestion about style(9) and
other style improvements:
- Since open(2) says that it returns -1 on errors,
explicitly determine whether it is returning -1
rather than whether the return value is less than
zero.
- Only set rval when there is no previous error.
This distinguishes the first error that occours.
- Use exit() in favor of return in main(), this is
suggested in old style(9), while the evolve has
fade the suggestion.
- Add some NOTREACHED comments.
- Add blank line after first { because no local variables
in usage()

Thanks to Ruslan for his tireless explaining of the code standards
and knowledge of the history of style(9).

[*] Pointy hat to: me

Submitted by: ru (with some minor changes)
Discussed with: ru, ssouhlal

In case of error, return errno, instead of 1.

Suggested by: delphij
Reviewed by: delphij
Approved by: grehan (mentor)

- Continue, in case of error.
- Add WARNS?= 6

Submitted by: Liam J. Foy <liamfoy@gmail.com>
Approved by: stefanf, grehan (mentor)

Consistently use FBSDID

Include missing header files which define functions for which gcc has
builtins (e.g., exit).

Submitted by: Mike Barcroft <mike@q9media.com>

Typos and spelling fixes.

Submitted by: charnier

Add fsync(8). This becomes useful with the advent of MAP_NOSYNC etc.

Reviewed by: peter