nrelease: Fix an annoying bug that was preventing the ISOs from booting UP.

nrelease: Fix an annoying bug that was preventing the ISOs from booting UP.

It seems our CD9660 support in libstand at least has some problems with
directory names containing dots. This prevented the LiveCD to properly
boot the UP kernel. Don't ask me about how it ended up using the SMP
kernel in this case, but that's what it did, making the UP boot
impossible. My guess is it has something to do with the order in which
stuff had been added to the ISO. But that's pure speculation. I'm not
even sure about the dot part. It might as well be directory name length.
In any case, UP boot from the LiveCD was broken.

To fix all this, install the UP kernel to /boot/UP and the SMP kernel to
/boot/SMP on the LiveCD and images. They will be picked up by the
installer from there by a separate commit.

While here, remove some non-functional code from dloader.menu. We can't
easily build i386/x86_64 dual boot ISOs at the moment (for this we would
need cross-building pkgsrc).

Thanks to sjg for bringing me on the right track.