Add new LOD Bias option, replacing option to always use highest detail models. New LOD Bias setting is shown in HUD/DEBUG and adjusted by auto-tuner in line with viewing distance tuning.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@2825 a9f3cfff-6c41-7446-b0ca-052bd761e6eb