(svn r8535) -Feature: Allow lumbermill to cut trees only when they are full grown.

This does not affect output of the mill, but make the visual aspect of it more accurate.
Prior of this, the mill produced cargo of the same amount even if the trees are on their first stages of growth.

src/industry_cmd.cpp

@@ -25,6 +25,7 @@
 #include "genworld.h"
 #include "date.h"
 #include "water_map.h"
+#include "tree_map.h"
 
 void ShowIndustryViewWindow(int industry);
 void BuildOilRig(TileIndex tile);
@@ -865,7 +866,7 @@ static void MaybePlantFarmField(const Industry *i)
  */
 static bool SearchLumberMillTrees(TileIndex tile, uint32 data)
 {
-	if (IsTileType(tile, MP_TREES)) {
+	if (IsTileType(tile, MP_TREES) && GetTreeGrowth(tile) > 2) { ///< 3 and up means all fully grown trees
 		PlayerID old_player = _current_player;
 		/* found a tree */
 
@@ -875,7 +876,6 @@ static bool SearchLumberMillTrees(TileIndex tile, uint32 data)
 		SndPlayTileFx(SND_38_CHAINSAW, tile);
 
 		DoCommand(tile, 0, 0, DC_EXEC, CMD_LANDSCAPE_CLEAR);
-		SetTropicZone(tile, TROPICZONE_INVALID);
 
 		_current_player = old_player;
 		return true;