Updated CREDITS and INSTALL, fixed Tomb:2 (David), fixed Xom's mutation-as-reward strategy.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@2683 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dshaligram  on October 30, 2007
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