filesystems within a pool

Add multiple inclusion protection.

PR:		165025
Submitted by:	Gavin Mu

Remove file system support based on the simple file system protocol.

MFC rev 201966:
Remove debugging printf().

This bring huge amount of changes, I'll enumerate only user-visible changes:

- Delegated Administration

	Allows regular users to perform ZFS operations, like file system
	creation, snapshot creation, etc.

- L2ARC

	Level 2 cache for ZFS - allows to use additional disks for cache.
	Huge performance improvements mostly for random read of mostly
	static content.

- slog

	Allow to use additional disks for ZFS Intent Log to speed up
	operations like fsync(2).

- vfs.zfs.super_owner

	Allows regular users to perform privileged operations on files stored
	on ZFS file systems owned by him. Very careful with this one.

- chflags(2)

	Not all the flags are supported. This still needs work.

- ZFSBoot

	Support to boot off of ZFS pool. Not finished, AFAIK.

	Submitted by:	dfr

- Snapshot properties

- New failure modes

	Before if write requested failed, system paniced. Now one
	can select from one of three failure modes:
	- panic - panic on write error
	- wait - wait for disk to reappear
	- continue - serve read requests if possible, block write requests

- Refquota, refreservation properties

	Just quota and reservation properties, but don't count space consumed
	by children file systems, clones and snapshots.

- Sparse volumes

	ZVOLs that don't reserve space in the pool.

- External attributes

	Compatible with extattr(2).

- NFSv4-ACLs

	Not sure about the status, might not be complete yet.

	Submitted by:	trasz

- Creation-time properties

- Regression tests for zpool(8) command.

Obtained from:	OpenSolaris

(link) address and the physical (load) address. Ideally, the mapping
between link and load addresses should be abstracted by the copyin(),
copyout() and readin() functions, so that we don't have to add kluges
in __elfN(loadimage)(). Then, we could also have paged virtual memory
for the kernel. This can be important under EFI, where you need to
allocate physical memory form the firmware if you want to work in all
scenarios.

loader so that it can memory can be allocated aligned at the beginning of
the desired large page

device (kind) specific unit field to the common field. This change
allows a future version of libefi to work without requiring anything
more than what is defined in struct devdesc and as such makes it
possible to compile said version of libefi for different platforms
without requiring that those platforms have identical derivatives
of struct devdesc.

means:
o  Remove Elf64_Quarter,
o  Redefine Elf64_Half to be 16-bit,
o  Redefine Elf64_Word to be 32-bit,
o  Add Elf64_Xword and Elf64_Sxword for 64-bit entities,
o  Use Elf_Size in MI code to abstract the difference between
   Elf32_Word and Elf64_Word.
o  Add Elf_Ssize as the signed counterpart of Elf_Size.

MFC after: 2 weeks