Raidctl -u ought to turn off autoconfigure on the target raid set

[buhrow%lothlorien.nfbcal.org@localhost (Brian Buhrow)]

        Hello.  I'm not sure if I should file this as a PR or simply make the
suggestion on the mailing lists.
        When raidctl -u is run against a raid set which has auto-configure
turned on, it really ought to first turn off autoconfigure on that raid set
before it unconfigures the raid set.  Otherwise, if you reboot the system,
the old raid set becomes a participant in the night of the living dead.
This can be a problem if you're trying to migrate from one image to another
by breaking a mirrored raid set, putting a new image on one of the disks,
configuring a new raid set with the newly imaged disk as the working
component, then rebooting to that new image and adding  the disk with the
old image to the new raid set and thus completing your upgrade.  When you
reboot, if the old disk is part of the original mirrored raid set, and the
new disk is part of a new raid set, you automatically boot to the old image
again.  Also, while it's possible to run raidctl -A no manualy before
unconfiguring the raid set, it would be nice not to have to remember that
step, or discover that you forgot it the hard way.

Just a thought.
-Brian