zroot won't mount after 9.0-RC2 -> 9.0-RELEASE upgrade

[Sergio de Almeida Lenzi]

Usually when upgrade,
I build it in the same machine,
1) csup -L 2 kernel.conf (build src on the new source/version)
2) cd /usr/src,  edit the kernel config....
3) make buildworld&&make buildkernel
4) make installworld installkernel
5) boot...

Using this set of commands I was able to upgrade from 8.x to 9.x  for
example
and the system boots (I use only zfs) with a setup like yours,
except that the root partition is at zfspool/root
so the boot.conf reads: vfs.root.mountfrom="zfs:zfspool/root"

For me, works...