zfs v28 destory -r snapshot failure

[Emil Muratov]

> 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.

Same here. zfSnap utility no longer purges old snaps since upgrading to 
v28. Manual testing discovered that zfs destroy -r no longer works as 
expected for snapshots, for datasets ok.