Changed horizontal location bullets are spawned.

The previous method was inconsistent between the left and right
directions; it placed the left edge of the bullet on the left edge of
the ship when going to the right, and in the center of the ship when
going left. This was barely noticeable with small ships, but more
noticeable with large ships. The method also sometimes made the backs
of bullets visible behind the smaller ships, which looked kind of
ugly.

Now, the back edge of the bullet is consistently placed in the center
of the ship.

src/bullets.cpp

@@ -32,7 +32,8 @@ void addBullet(object *theWeapon, object *attacker, int y, int dy)
 
 	bullet->next = NULL;
 	bullet->active = true;
-	bullet->x = attacker->x - ((attacker->image[0]->w / 2) * attacker->face);
+	bullet->x = attacker->x + (attacker->image[0]->w / 2) -
+		(theWeapon->image[0]->w * attacker->face);
 	bullet->y = attacker->y + y;
 	bullet->flags = theWeapon->flags;
 	bullet->shield = 300; // bullets live for (approximately) 5 seconds