MFC r325035: MFV r325013,r325034: 640 number_to_scaled_string is duplicated in several commands

FreeBSD note: of all libcmdutils functionality ZFS (and other illumos
contrib code) currently uses only nicenum() function (which is similar
to humanize_number but has some formatting differences). For this
reason I decided to not port the whole library. As a result, nicenum.c
from libcmdutils is compiled into libzfs and libzpool. This is a bit
ugly, but works. If one day we are forced to create libillumos, then
the file should be moved to that library.

MFC r305206: MFV r302658:
6872 zfs libraries should not allow uninitialized variables

illumos/illumos-gate@f83b46baf98d276f5f84fa84c8b461f412ac1f5e
https://github.com/illumos/illumos-gate/commit/f83b46baf98d276f5f84fa84c8b461f41
2ac1f5e

https://www.illumos.org/issues/6872
We compile the zfs libraries with -Wno-uninitialized. We should remove
this. Change makefiles, fix new warnings, fix pbchk errors.

Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Prakash Surya <prakash.surya@delphix.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Paul Dagnelie <pcd@delphix.com>

MFC r305207: MFV r302659: 6931 lib/libzfs: cleanup gcc warnings

illumos/illumos-gate@88f61dee20b358671b1b643e9d1dbf220a1d69be
https://github.com/illumos/illumos-gate/commit/88f61dee20b358671b1b643e9d1dbf220a1d69be

https://www.illumos.org/issues/6931
need cleanup:
CERRWARN += -_gcc=-Wno-switch
CERRWARN += -_gcc=-Wno-parentheses
CERRWARN += -_gcc=-Wno-unused-function

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Igor Kozhukhov <ikozhukhov@gmail.com>

MFC r277300 (by smh): Mechanically convert cddl sun #ifdef's to illumos

Since the upstream for cddl code is now illumos not sun, mechanically
convert all sun #ifdef's to illumos #ifdef's which have been used in all
newer code for some time.

Also do a manual pass to correct the use if #ifdef comments as per style(9)
as well as few uses of #if defined(__FreeBSD__) vs #ifndef illumos.

MFC r289562: 6328 Fix cstyle errors in zfs codebase

Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Alex Reece <alex@delphix.com>
Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed by: Jorgen Lundman <lundman@lundman.net>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Paul Dagnelie <pcd@delphix.com>

illumos/illumos-gate@9a686fbc186e8e2a64e9a5094d44c7d6fa0ea167

MFC r289497: 5745 zfs set allows only one dataset property to be set at a time

Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Bayard Bell <buffer.g.overflow@gmail.com>
Reviewed by: Richard PALO <richard@NetBSD.org>
Reviewed by: Steven Hartland <killing@multiplay.co.uk>
Approved by: Rich Lowe <richlowe@richlowe.net>
Author: Chris Williamson <chris.williamson@delphix.com>

illumos/illumos-gate@30925561c223021e91d15899cbe75f80e54d8889

MFC r288340: define aok in libnvpair which is linked to all zfs
libraries that need aok

MFC r264835 (MFV r264829):

3897 zfs filesystem and snapshot limits

MFC r264835 (MFV r264829):

3897 zfs filesystem and snapshot limits