PATCH: teach (gpt)zfsboot, zfsloader to discern vdev status correctly

[Xin LI]

Hi, Matt,

I have committed your proposed change with slight space changes (some
space -> tab to fit nearby code style, and no blank line after and
before if's { }), with a MFC set of 2 weeks.

Thanks for the submission which makes FreeBSD better!

Cheers,
-- 
Xin LI <delphij at delphij.net> http://www.delphij.net