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

Pull up fixes to allow building tests along scripts and data files.

MFC of the following into stable/10:
- r257095 Allow mixing bsd.files.mk with bsd.subdir.mk.
- r258095 Allow this (bsd.progs.mk) to work with fmake.
- r258330 Need to also test for defined(${v}_${PROG}) in bsd.progs.mk.
- r259209 Make bsd.progs.mk work in directories with SCRIPTS but no PROGS.

This is all 'make tinderbox' clean as run on ref10-amd64.

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

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

Pass more variables to bsd.prog.mk and
only append to already defined variables.

Submitted by: Garrett Cooper

Latest progs.mk from crufty.net for ATF

Approved by: marcel (mentor)

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@