Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

MFC r237624, r237714, r237716, r237860:

Bring llquantize support into Dtrace.

Bryan Cantrill implemented the equivalent of semi-log graph
paper for Dtrace so llquantize will use one logarithmic and
one linear scale.

Import the dtrace llquantize test files from the vendor area.

Now that we have an illumos vendor area, import the llquantize
test files directly from there to make it easier to track the
code provenance.

Special thanks to Martin Matuska for populating the illumos
vendor area.

Requested by: obrien

Update illumos/dist to revision 13742:b6bbdd77139c
ZFS bits will follow in a separate commit