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

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

DTrace: re-merge remainder of r249367 (original from Illumos).

Bring back some important fixes from Illumos:

3022 DTrace: keys should not affect the sort order when sorting by value
3023 it should be possible to dereference dynamic variables
3024 D integer narrowing needs some work

We particularly avoid the LD_NOLAZYLOAD changes that Illumos made
as those don't apply to FreeBSD and were causing problems in
interactive mode.

Illumos Revision: 13758:23432da34147

Reference:

https://www.illumos.org/issues/3022
https://www.illumos.org/issues/3023
https://www.illumos.org/issues/3024

MFC after: 1 month
Tested by: markj

Update vendor/illumos to illumos-gate 13758:23432da34147 (dtrace changes)

References:
https://www.illumos.org/issues/3021
https://www.illumos.org/issues/3022
https://www.illumos.org/issues/3023
https://www.illumos.org/issues/3024
https://www.illumos.org/issues/3025
https://www.illumos.org/issues/3026

Obtained from: ssh://anonhg@hg.illumos.org/illumos-gate