Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

Add the undocumented -R option to disable randomness for regression-testing.

Add a couple of simple regression tests accessible with "make test", they
depend on the md(4) driver.

FYI I have also tried running the test against a week old newfs and it
passed.