With this, one can use its self-replacement code (which copies a bunch of its state into the replacement actor, and monitors for boss death if appropriate), but select the replacement class based on some other criteria (map number, the player's RPG stats, the player's class, etc).
(cherry picked from commit ce1aa7e962)
Previously, a RandomSpawner with infinite recursion would hang the game, because the recursion check was happening before the recursion counter (bouncecount) was set.
(cherry picked from commit 6239796b92)
