New experimental "Use model instancing" option which uses hardware instancing to reduce draw calls on repetative scenes. The option only works when "Always use highest detail objects" is selected (for now).
Also add "Vertical sync" option to video tab.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@2148 a9f3cfff-6c41-7446-b0ca-052bd761e6eb