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

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

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

Make this sample build again.

Sample modules for KLD.

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