More bugfixes from OpenSolaris

[Martin Matuska]

 Hi, I have the following changesets from OpenSolaris upstream that I
would like to propose to import to head and after v15 merge to stable/8.
The code resulting from these bugfixes has not been changed in
OpenSolaris by today (matches pjd p4 tree).

1.) revision 9788:f660bc44f2e8 (possible memory corruption on zfs umount)
zfs_znode_move() does not ensure valid file system pointer
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6843700
http://mfsbsd.vx.sk/zfs/head-9788.patch

2.) revision 9909:aa280f585a3e (locking bugfix - affects zfs rollback)
zfs related assertion failure: vp->v_filocks == 0L, file:
../../common/fs/vnode.c, line: 2344
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6790232
http://mfsbsd.vx.sk/zfs/head-9909.patch

3.) revision 9847:2f3ba86e857a (feature)
snapshots should be considered as descendants via zfs allow -d
http://bugs.opensolaris.org/bugdatabase/view_bug.do?bug_id=6809340
http://mfsbsd.vx.sk/zfs/head-9847.patch

Patches are direct OpenSolaris imports and apply cleanly.