(svn r1640) fix: now helicopters will use a hangar in schedule to be replaced in, even if they are only set to service there. Since helicopters are serviced at helipads, they will only go there if they needs to be replaced or renewed.

static const byte _dir_to_straight_trackdir[4] = {
	0, 1, 8, 9,
};

static const byte _reverse_dir[4] = {
//	3, 0, 1, 2
	2, 3, 0, 1
};