makes booting more reliable (and working at all on USB sticks). While here,
move responsibility for setting up fstab into the various platform mk-*.sh
scripts.
Suggested by: many
i386 and amd64. This involved moving the memstick generation script to
the arch directories from scripts/, in analogy to mkisoimages.sh. This
script was never called from /usr/src/release/Makefile, so that hasn't
been updated.