DieselEngine start/stop logic added - ControlDieselPlayer and ControlDieselHelper added to control player and helper locomotive diesel engine separately. Remember that diesel engine can be started/stopped only if throttle is set to zero.
git-svn-id: http://svn.uktrainsim.com/svn/openrails/trunk@970 a9f3cfff-6c41-7446-b0ca-052bd761e6eb