Synchronize releng/9.2 Forth code with stable/9 via MFS of 2 revisions:

First, MFS of SVN r254109: itself an MFC of 22 revisions:
227727, 233941, 235560, 238431, 241310, 241361, 241363, 241365, 241367,
241523, 242667-242669, 242923, 243114, 243660, 244048, 244089, 244158,
253715, 254105, and 254108.

This includes critical fixes that sadly should have been merged prior.
Namely, SVN r244158 fixes a possible regression.

Second, MFS of SVN r254146: Itself an MFC of r242688.

Approved by:	re (marius)
MFC 254132, 254270:
  Add empty zones for Shared Address Space (RFC 6598)

Approved by:  re (glebius), delphij (mentor)
Sponsored by: DK Hostmaster A/S
MFC: Temporarily revert sendmail 8.14.7 change to getipnodebyname() flags
     to prevent problems between the resolver and Microsoft DNS servers with
     AAAA lookups.  The upstream open source project will work on a more
     permanent fix for the next release.  Issue noted by Pavel Timofeev.

Approved by:	re (glebius)
MFC r254352:
Don't send uninitialized memory (two instances of 4 bytes) in
every cookie on the wire. This bug was reported in
https://bugzilla.mozilla.org/show_bug.cgi?id=905080

Approved by:	re@
MFC r253853:
  Include /usr/local/etc/libmap.d/ by default.

  PR:             180568
  Reviewed by:    bapt
  Obtained from:  kib

Approved by:      re (delphij)
MFC r254265:
 Make sure bootonly.iso for -BETAs and -RCs use the releases/
 directory on the FTP mirrors to fetch distributions, since
 these are always pushed to releases/ during the release cycle.

Approved by:	re (marius)
 Merge r254306:

 Update PCI drivers to no longer look at the MEMIO-enabled bit in the PCI
 command register.  The lazy BAR allocation code in FreeBSD sometimes
 disables this bit when it detects a range conflict, and will re-enable
 it on demand when a driver allocates the BAR.  Thus, the bit is no longer
 a reliable indication of capability, and should not be checked.  This
 results in the elimination of a lot of code from drivers, and also gives
 the opportunity to simplify a lot of drivers to use a helper API to set
 the busmaster enable bit.

 This changes fixes some recent reports of disk controllers and their
 associated drives/enclosures disappearing during boot.

Submitted by:	jhb
Reviewed by:	jfv, marius, adrian, achim
Approved by:	re
Merge r254366:
  Make the check for number of entries less strict.
  Some partitioning tools can create GPT with number of entries less
  than 128.

Approved by:	re (marius)
Update releng/9.2 to -RC2.

Approved by:	re (implicit)
MFS9 SVN r254331:
Add optional support for default override of standard setup; but only if
corresponding functions are provided. If override function does not exist,
boot remains unmodified. This patch should not result in any changes.

This includes changes to take advantage of the new functionality.

Approved by:	re (marius)