Cell SPU file system, snapshot 4

Thankfully, there is now documentation available to the world about the Cell architecture (http://cell.scei.co.jp/e_download.html), so I am now able to disclose more of our work on the SPU file system.

This is a rather big update compared to the previous version, as it contains work from Mark Nutter and Ulrich Weigand to support context save and restore of SPUs. This release should still be fully compatible to the previous ones, but we intend to do incompatible changes for in the future.

	Arnd <><