Change Trog's retribution to send berserking monsters instead of normal

ones after you. The points system from the old code is still used to get the power level for summon_berserker(), and the "quick reduction for large values" now takes off 20 points instead of 15 to compensate for the monsters' being stronger.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@2915 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on November 26, 2007
JOE4G4IU6O64WRW4CYDALGFCN6XHDI57MGLBBDHS4KHFLAH473PAC
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