Add Yred retribution effect: if there are corpses around, animate them

as hostile zombies.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@7569 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on November 23, 2008
S6SXU7V43LLW545J72DST5LADMPT36DDHZZXUBIJXRQRSMUCJMKAC
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