3D sorting + bugfix

[Andrew Davie]

In this rather long video I'm demonstrating the much improved stability of the 3D engine. Here it's running 10 spaceships. Previously I had been displaying only the back-faces (!!!) of the objects, so things were kind of warped and weird. Now that's fixed -- I kind of stumbled on this issue and am glad to have it working.  I have also found/fixed an issue with crashes which was caused by trying to render pollys that had been classified as "off screen". This lead to infinitely long lines being drawn and consequent overtimes.  There really isn't a lot of time available to do all this stuff - it all happens in the overblank (overscan+vertical blank) of a TV frame.

[Andrew Davie]

There is a bug in quicksort - so I'm actualy using *gasp* bubble sort *gasp* in this version. Here I'm running 12 ships. A few issues still with the screen/polys, but getting there.