Implement FR 1928421: let Snorg go berserk!

There's a flat 5% chance of Snorg going berserk each turn an enemy (you or an ally) is in sight. Once he is wounded, even if just by a scratch, that chance increases to 20% per turn.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@5795 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on June 13, 2008
RI66KX7UKHLUZR4GK6Z7T3CCRVJWXTQOIWMPWQ5TULMYFBCWISRAC
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