This is actually different than the original, but hopefully the
normalisation will not break things, as it's more liberal than strict.

we also fix the disk names.

I was hesitant here; i'm not sure an encrypted pool is the right
approach anymore, because:

16:56:10 <PMT> notably, because you can't recv -F onto or from encrypted things, you couldn't, say, ever do send -R rpool@latestsnap | recv -F newrpool

... and `recv tank` is pretty much exactly what i'm aiming to do in
the long term here.

But worst case, i can just rebuild a new tank, that's easy. It's
trickier for rpool though.

dang you ikiwiki