zfs v28 destory -r snapshot failure

[John]

Applied this patch set stable-8-zfsv28-20110501.patch.xz to a fresh download
of 8.2-release, buildworld, buildkernel, install and rebooted. Did not upgrade
pool or filesystems.

Made a snapshot of tank/foo at today, then tried to delete with
zfs destroy -r tank at today yielded:
cannot destroy 'tank at today': dataset does not exist
no snapshots destroyed

If tank at today exists along with tank/foo at today, then the destroy works
correctly.

Rebooted with kernel.old which is 8.2-release without the v28 patch and
zfs destroy -r tank at today deleted tank/foo at today without an error.

John Theus