Initial ZVOL work, most filesystems can be put on ZVOL, but not HFS and
no disk arbitration
Extra root check, and compile fixes.
Apparently bdevsw's "psize" *has* to return 512, not the actual blocksize.
We also did not release EXCL open after close, so device only worked once.
Add new PlugIns kext for missing kernel exports. This needs verification that
it works on 10.6 / 10.7.
Fix ZVOL work, and integrate with SPL sunddi.
Fix zfs send/recv to work with pipes.