Trying to add support for OSX on virtualbox

So don't merge this one just yet... I haven't gotten it *totally* working
yet. This PR is a WIP, and a plea to the community for some help getting
it working.  Here's a screenshot to show how close I've gotten:

![So close...][img]


Almost there!  I believe the problem is that the darwin kernel does not
recognize the root disk .vdi that VirtualBox has connected.
If anyone knows how to trick OSX into recognizing the disk or SATA
controller correctly, help would be appreciated!

[img]: https://clbin.com/LBaTIo.png "Booting OSX 10.8.4 on VirtualBox"