Nerudite bow tweak

Nerudite bow had a spellpower penalty of 0, rather than -30 like battle
bows. That really didn't make sense (nerudite is supposed to be
antimagic), and it was also incredibly powerful for veterans.

This puts nerudite bows at -30 power penalty, but increases their chance
to shatter nerudite arrows, which is what everyone always thought they
did before we got a look at the code. This change equates to 30% higher
chance to add 1-2 damage. Shouldn't break anything, but is not at all
shabby.

viShatter_chance is also now a variable on nerudite bows for creative event admins.

People will defend nerudite bows based on their rarity, but that doesn't really follow. There are dozens in existence because 101 is so old, and we shouldn't really let people have super weapons just because the item is rare.