lxdream WIP - Small fixes

Progress on the Sega Dreamcast emulator for PC.

Mostly just finishing/unbreaking things I’d broken in recent changes, so there’s nothing terribly exciting to report at the moment.

Changes

* Fix launching from the Finder (odd command line arguments and all)
* Move the background into the main scene structure, so it’s actually included in the min/max z (the lack of which was causing missing backgrounds in some situations). Massively simplifies things at the cost of needing colour unclamping support for correct output in all situations.
* Change internal colour format to float from unsigned char - surprisingly doesn’t have much impact on performance, but makes a few things much simpler to implement
* Finish integrating the run-time limiting properly so that it’s no longer a big wart on main.c (and works properly on OS X as well)
* Refactor the GD-Rom selection menu to be a bit more generic and add a cocoa view for it