MFV r252839:

Quoting illumos issue #3836:
  Currently zio_free() always puts the zio on a list for subsequent
  processing by zio_free_sync().  This is only necessary for frees that
  might need to issue reads (gang and dedup blocks).

  By processing the majority of the frees as we encounter them, we reduce
  the amount of time that the spa_sync() thread spends burning CPU and
  not doing any i/o, thus increasing the overall write throughput of the
  system.

Illumos ZFS issues:
  3836 zio_free() can be processed immediately in the common case

MFC after:	1 week
Add new privileges, PRIV_KMEM_READ and PRIV_KMEM_WRITE, used in opening
/dev/kmem and /dev/mem (in addition to traditional file permission checks).
PRIV_KMEM_READ is different from other PRIV_* checks in that it's allowed
by default.

Reviewed by:	kib, mckusick
Remove superfluous continue at end of loop. (pointy-hat)
Add the necessary code to reinstall packages. Both scripted access
(packageReinstall) and UI access have been tested successfully with a
variation of different situations including:
+ Reinstall a package for which no other packages depend
+ Purposefully do thinks like reinstall a package that is not installed
+ Try to reinstall a package which other installed packages still depend

NOTE: There is no "force" used; if a package is required by other packages,
it will not be uninstalled (and therefore no reinstall is done).
Bump up _PRIV_HIGHEST to account for PRIV_KMEM_READ/WRITE.

Submitted by:	mdf
- Add SRC_FORCE_CHECKOUT configuration option to force svn to checkout
  the src/ tree into a directory that contains files/directories, such
  as a case where a custom kernel configuration file is specified.

- Allow specification of multiple KERNCONFs to pass to 'make release'.

- Move evaluation of NODOCS/NOPORTS earlier, and set based on how the
  release process expects these options to be evaluated.

- Wrap KERNCONF specification in double quotes, and use 'eval' so multiple
  kernel configurations do not cause the build to fail in strange ways.

- Set WITHOUT_X11 for the port build flags for the documentation toolchain
  build.  Also run 'clean distclean' targets during port build.

PR:		180192
Submitted by:	Anes Mukhametov
MFC after:	3 days
Approved by:	kib (mentor, implicit)
Add a missing unlock.