- fix the reinstallation (preserve-/home) option;
- remove support for just reinstalling the bootloader, as the main
purpose of this option (allowing an upgrade from the old MINIX
boot monitor to the NetBSD bootloader) is no longer needed and was
already broken;
- do not try to copy over /etc/motd.install: it no longer exists.
This resolves issue 106.
Change-Id: Iad3805d86c4806d725f9b285c2d4378670790f78