Man zpool missing param - but unclear scope and best fix

[Stilez]

I just learned that <zpool> has a rather useful "-D" option that's not in 
the man page. So the docs need fixing.

But I'm not clear what the correct text would be (it's not documented in 
the first place), and it's also worth a wuick check that no other 
undocumented options exist for the zpool/zfs commands.

Maybe someone more experienced can check the source code and fix this? It's 
beyond my knowhow. Or I can add it to the tracker, but I suspect asking 
here will be more efficient.

Thanks.