Bug#260649: grub-installer: ask grub-installer/with_other_os at critical priority?

[Petter Reinholdtsen <pere@hungry.com>]

[Colin Watson]
> Perhaps this should be asked at critical instead?

I think dual boot scenarios should be considred special enough to
expect people to run on priority high or lower if they want that to
work.  Critical should be used for questions where the default will
work for most people, not for questoins which might fail for some
people.

And if the boot loader is goofed up, one can rerun the installer with
a lower priority to fix it.  No need to raise the priority of this
question to fix it.

Debian-edu raised the priority to critical to get away with all the
questions where the default is fine.  We don't want the to pop up
again at priority critical too.  In fact, I would like to be able to
install debian-edu using priority high, and lower the priority of all
the questions with a default which work for most installs.