Merge http://mail-index.netbsd.org/source-changes/2014/01/10/msg050660.html

RCS Id update.
More updates to pass boothowto and boot device info to kernel.

- make boot command parse boothowto flags (-ads etc.)
- pass boothowto and bootdev info to the kernel via %d7 and %d6
  as the old 4.4BSD/luna68k kernel expected
- remove unused and now unnecessary "howto" (how_to_boot) command
- export and tweak make_device() in devopen.c to prepare bootdev info
- remove unused and commented out get_boot_device()

Note this change requires updated <machine/bootinfo.h> (not in this repo).