Mollusk Creature upgrade

Mollusk creatures were rather bland and unfinished. They've been given
proper AI behavior and a speed upgrade. As a result, they can have
rather deadly spikes in damage with thrown rocks - the safest place when
fighting a Mollusk Creature is up close, where it is forced to use its
slower claw attack. Mollusks WILL try to move away from you as you fight
in order to reach optimal range for throwing rocks. Don't let them.

Mollusk Creatures are AI_FIGHT_NEWBIESAFE now, so those 50 and under can
travel through their area safely.

Even so, I'm pretty sure some people are going to die to Mollusks.