Fix cowbell.

* As per Christopher Walken's reasearch, ringing cowbell repeatedly can
  provide a minor morale boost (1).
* 1: Later research has shown that this becomes up to an order of magnitude
  more effective in test subjects exposed to high doses of bovine mutagen

* OOC: 1/2 chance of +1 morale up to 15. chance and cap scales up with MUTCAT_CATTLE,
  up to 10 in 11 chance and a 150 morale cap
* Yes this is incredibly silly...but cow bell!
* Morale boost for a heavily cattle mutated character isn't excessive,
  the poor sap is turning into a cow and could use a break.