Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

- Fix style(9) a bit
-- Fix whitespace
-- Use err/errx
-- Remove superfluous braces
- Be a bit more defensive with input from the end-user
- Don't throw a floating point exception by dividing by 0 when processing a
zero-byte file

MFC after: 1 week

NO_MAN= has been deprecated in favor of MAN= for some time, go ahead
and finish the job. ncurses is now the only Makefile in the tree that
uses it since it wasn't a simple mechanical change, and will be
addressed in a future commit.

Include a very basic (and beta) tool for stressing disks using the POSIX
AIO calls.

This small program queues up a controllable number of concurrent AIO
read operations w/ controllable io size against a disk or regular file.
There are a few other things to add (notably optional write support!)
but it works well enough at the present time to stress the AIO code out
relatively harshly in the disk IO case.