lxdream WIP - Render branch merged back to trunk

Progress on the Sega Dreamcast emulator for Linux.

There’s some outstanding niggles with the transparency auto-sorting (which will be fixed when I beef up the sorting algorithm), but by and large I think I’ve fixed everything I broke with the render changes. So that’s merged back to trunk now where the rendering work will continue. The big win so far has been fixing perspective correction - by itself that’s fixed something like 95% of the visual problems I was seeing.

Time to do some more rendering features now I think ^_^
Changes

* Fix perspective-correction (shader-only at the moment)
* Change mip-map texture loading to work around bug in ATI drivers
* Add mirrored texture support
* Add configure checks for fbo + shader support (to avoid linking errors on really old GL libraries)