Adds zpool split to man page

Adds zpool split documentation to the zpool man page.  I only documented
the options that I could get to work.   While it is documented on some
sun blogs that devices can be specified for split, I was not able to get
that to work during my testing.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1456
Don't leak mount flags into kernel

When calling mount(), care must be taken to avoid passing in flags
that are used only by the user space utilities.  Otherwise we may
stomp on flags that are reserved for other purposes in the kernel.

In particular, openSUSE 12.3 kernels have added a new MS_RICHACL
super-block flag whose value conflicts with our MS_COMMENT flag. This
causes incorrect behavior such as the umask being ignored.  The
MS_COMMENT flag essentially serves as a placeholder in the option_map
data structure of zfs_mount.c, but its value is never used. Therefore
we can avoid the conflict by defining it to 0.

The MS_USERS, MS_OWNER, and MS_GROUP flags also conflict with reserved
flags in the kernel. While this is not known to have caused any
problems, it is nevertheless incorrect.  For the purposes of the
mount.zfs helper, the "users", "owner", and "group" options just serve
as hints to set additional implied options.  Therefore we now define
their associated mount flags in terms of the options that they imply
rather than giving them unique values.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1457
Added arcstat.py from FreeNAS

Original source:
  http://support.freenas.org/browser/nanobsd/Files/usr/local/bin/arcstat.py

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1506
Modified arcstat.py to run on linux

* Modified kstat_update() to read arcstats from proc.
* Fix shebang.
* Added Makefile.am entries for arcstat.py

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1506
Improve OpenRC init script

The current zfs OpenRC script's dependencies cause OpenRC to attempt to
unmount ZFS filesystems at shutdown while things were still using them,
which would fail. This is a cosmetic issue, but it should still be
addressed. It probably does not affect systems where the rootfs is a
legacy filesystem, but any system with the rootfs on ZFS needs to run
the ZFS init script after the system is ready to shutdown filesystems.

OpenRC's shutdown process occurs in the reverse order of the startup
process. Therefore running the ZFS shutdown procedure after filesystems
are ready to be unmounted requires running the startup procedure before
fstab. This patch changes the dependencies of the script to expliclty
run before fstab at boot when the rootfs is ZFS and to run after fstab
at boot whenever the rootfs is not ZFS. This should cover most use
cases.

The only cases not covered well by this are systems with legacy
root filesystems where people want to configure fstab to mount a non-ZFS
filesystem off a zvol and possibly also systems whose pools are stored
on network block devices. The former requires that the ZFS script run
before fstab, which could cause ZFS datasets to mount too early and
appear under the fstab mount points. The latter requires that the ZFS
script run after networking starts, which precludes the ability to store
any system information on ZFS. An additional OpenRC script could be
written to handle non-root pools on network block devices, but that will
depend on user demand and developer time.

Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1479