(svn r19137) -Add: Report a more useful error when failing to build a bubble generator.

src/industry_cmd.cpp

@@ -1251,7 +1251,11 @@ static bool CheckNewIndustry_Lumbermill(TileIndex tile)
  */
 static bool CheckNewIndustry_BubbleGen(TileIndex tile)
 {
-	return GetTileZ(tile) <= TILE_HEIGHT * 4;
+	if (GetTileZ(tile) > TILE_HEIGHT * 4) {
+		_error_message = STR_ERROR_CAN_ONLY_BE_BUILT_IN_LOW_AREAS;
+		return false;
+	}
+	return true;
 }
 
 /** Industrytype check function signature.

src/lang/english.txt

@@ -3386,6 +3386,7 @@ STR_ERROR_CAN_ONLY_BE_BUILT_IN_TOWNS_WITH_POPULATION_OF_1200    :{WHITE}... can
 STR_ERROR_CAN_ONLY_BE_BUILT_IN_RAINFOREST                       :{WHITE}... can only be built in rainforest areas
 STR_ERROR_CAN_ONLY_BE_BUILT_IN_DESERT                           :{WHITE}... can only be built in desert areas
 STR_ERROR_CAN_ONLY_BE_BUILT_IN_TOWNS                            :{WHITE}... can only be built in towns
+STR_ERROR_CAN_ONLY_BE_BUILT_IN_LOW_AREAS                        :{WHITE}... can only be built in low areas
 STR_ERROR_CAN_ONLY_BE_POSITIONED                                :{WHITE}... can only be positioned near edges of map
 STR_ERROR_FOREST_CAN_ONLY_BE_PLANTED                            :{WHITE}... forest can only be planted above snow-line