[patch] add GNU/kFreeBSD fstab and init

[Luca Favatella <slackydeb@gmail.com>]

This patch adds GNU/kFreeBSD /etc/fstab and /sbin/init.
Please carefully review it.

I'm proposing both together because they are closely related.

This patch should not affect GNU/Linux builds and has been in the
kfreebsd d-i branch for a while.


Cheers,
Luca Favatella