optimize vehicles:

   cache vehicle::parts_at_relative which accounted for 50% of the delay in do_turn
   link vehicle_part to vehicle_part_info via integer index
   vehicle_part_info::has_flag takes string or int; string flags are auto added to bitmask, if their usage
      warrants such

Why? Because wait is hellaciously slow due to http://i.imgur.com/00NoXro.png