4 commits for freebsd 9.2 zpool features

fixes #26

NB:

1. I'm pretty new to FreeBSD YMMV etc
2. sha: #81c59d4 might not be appropriate but I saw references to this on several posts, please let me know what's best
3. lzjb and other features should probably be tested using the zfs feature stuff, I'm not sure how to do this & > 28 seem like a reasonable hack