EFI/ZFS Update: successful tests, need more complex vdevs

[Steven Hartland]

Just wanted to let everyone know that I just finished committing these 
changes to the tree.

Huge thanks to Eric's for his work on this, as well as everyone else who 
contributed.

I've set the target for MFC of 2 weeks, so I hope to be able to get this 
into stable/10 before the 10.3 slush, so if you're interested in this 
change please test a head build > r294068 ASAP.

     Regards
     Steve