Cleaned up ability damage equation

It was just ugly before. Now that I better understand how Meridian
truncates, this should be a smoother curve.
Removed needless code in Zap

Zap had duplicate PlayerWasHitMsg for some reason. Deleted it.
Mysticism stat bonus damage added

Added Mysticism bonus damage the way that touch spells get bonus damage
(and melee weapons get from Might, etc).

Splash and bolt spells can now do drastically increased base damage if
you have enough Mysticism.

Also fixed fire and lightning wall damage types so that Resist Magic
works against them.