horizontal const-z rendering test, part 2

testing a new feature for 486quake, where perfectly horizontal surfaces can be detected and optimized with a constant-z rendering algorithm (a la snes's mode7 graphics, or how doom renderer works) this is testing only the detection - surfaces that could be optimized are rendered in plain grey instead of their normal texture. this recording is done with cl_rollangle set to 0, which disables part of the view bobbing done by quake - the optimization is able to happen more often with this off.