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

Update fifolog internals to match main version:

Rename ...write_bytes... to ...write_records..., that's what they do.

Move writer .h stuff into writer private .h file.

Change logic in writer to support both fifolog usage in FreeBSD and
Measured usage better, by always using an input buffer.

Various cleanups.

Add the fifolog tools to FreeBSD.

Quoth the man-page:

Fifologs provide a compact round-robin circular storage for recording
text and binary information to permanent storage in a bounded and pre-
dictable fashion, time and space wise.

Not yet connected to the build, but feel free to test & review.