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

Include unistd.h for read(), write() and stdlib.h for exit().
Bump WARNS to 5 while being here.

Fix the cdev kld example.

PR: 52954
Submitted by: Priit Piipuu <priit.piipuu@mail.ee>
Reviewed by: phk

Add `_PATH_DEVZERO'.
Use _PATH_* where where possible.

Fix cdev kld example after it has been broken for year or so. Also extend list
of supported operations by example read() and write() operations.

Inspired by: http://www.daemonnews.org/200010/blueprints.html
PR: 16173
Submitted by: sobomax

* Tidy up a few things and fix some more warnings.
* Change the devsw declaration to standard form and add missing fields
* Change the filename from cdev_mod.ko to cdev.ko

Sample modules for KLD.

PR: misc/8621
Submitted by: Rajesh Vaidheeswarran <rv@fore.com>