Preserve the player's looking direction

Contributed by @gpcf

advtrains/wagons.lua

@@ -477,6 +477,28 @@ function wagon:on_step(dtime)
 				self.object:setpos(actual_pos)
 			self.object:setvelocity(velocityvec)
 			self.object:setacceleration(accelerationvec)
+			
+			if #self.seats > 0 and self.old_yaw ~= yaw then
+			   if not self.player_yaw then
+			      self.player_yaw = {}
+			   end
+			   for _,name in pairs(self.seatp) do
+			      local p = minetest.get_player_by_name(name)
+			      if p then
+				 if not self.turning then
+				    -- save player looking direction offset
+				    self.player_yaw[name] = p:get_look_horizontal()-self.old_yaw
+				 end
+				 -- set player looking direction using calculated offset
+				 p:set_look_horizontal(self.player_yaw[name]+yaw)
+			      end
+			   end
+			   self.turning = true							 
+			elseif self.old_yaw == yaw then
+			   -- train is no longer turning
+			   self.turning = false
+			end
+			
 			self.object:setyaw(yaw)
 			self.updatepct_timer=2
 			if self.update_animation then