Replaced is_player_visible() with is_agent_visible()
Security bots as part of their turn get a chance to recognize a controlled
robot and if they do it becomes their main target. As part of this, when a
monster is killed, set clear out anywhere they were the last_attacker or
target. (This entails me looping over every monster on every level, which
if it gets too slow I'll have to make more clever)
ED209 can now recognize the player controlling a bot. Also, Shooter-based
monsters now pick a target and go after it, rather than explicitly
choosing to target dm.player.
Predator drones and docbots now recognize the player if they are
remote-controlling a robot and go after them. The other Bot classes I am
okay with their current behaviour, I think.