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 ATF to the build. This is may be a bit rought around the egdes,
but committing it helps to get everyone on the same page and makes
sure we make progress.

Tinderbox breakages that are the result of this commit are entirely
the committer's fault -- in other words: buildworld testing on amd64
only.

Credits follow:

Submitted by: Garrett Cooper <yanegomi@gmail.com>
Sponsored by: Isilon Systems
Based on work by: keramida@
Thanks to: gnn@, mdf@, mlaier@, sjg@
Special thanks to: keramida@