Add isboot iSCSI boot driver to FreeBSD

Hi,

isboot is a iSCSI boot driver written by Daisuke Aoyama that allows you 
to boot your root partition using iSCSI.

Installation is extremely simple:

1. extract the archive:
     # tar zxvf isboot-x.x.x.tar.gz

2. compile the module:
     # cd isboot-x.x.x/src
     # make

3. install the compiled module to the kernel directory:
     # make install

4. edit /boot/loader.conf, and add the following line:
     isboot_load="YES"


This was first announced way back in June, 2010:

https://lists.freebsd.org/pipermail/freebsd-scsi/2010-June/004425.html


I've tested the current version (v0.2.10) and it works with FreeBSD 10.2 
booting a ZFS on root installation:

http://www.peach.ne.jp/archives/isboot/isboot-0.2.10.tar.gz


I've used iSCSI boot with Ubuntu Server for a while and it's been very 
useful. I'm looking forward to FreeBSD having the same capability built-in.

Cheers,
Yonas