MFC r326276:

various: general adoption of SPDX licensing ID tags.

Mainly focus on files that use BSD 2-Clause license, however the tool I
was using misidentified many licenses so this was mostly a manual - error
prone - task.

The Software Package Data Exchange (SPDX) group provides a specification
to make it easier for automated tools to detect and summarize well known
opensource licenses. We are gradually adopting the specification, noting
that the tags are considered only advisory and do not, in any way,
superceed or replace the license texts.

No functional change intended.

Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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.

Fix a bunch of trivial whitespace mistakes and update the miniobj.h
file before the real work starts.

Unify fifolog_writer usage printout with fifolog_create and
fifolog_reader.

Approved by: trasz (mentor)

Populate usage()

Submitted by: Jaakko Heinonen <jh@saunalahti.fi>

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.