Adjust the probability of summoning very ugly things again. It now

properly goes up with spell power for players, or with hit dice for monsters.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@4388 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on April 19, 2008
MHHBLKFDEKM5CJ55ZCCFJEI4QH3WVLX673FWNJMXAKBG4FHXG4DAC
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