Ensure the the Helix card only removes bad mutations, and that Zin's

retribution only removes good mutations, by adding a parameter to delete_mutation() to disallow mismatches of random good and bad mutations.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@10287 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on July 18, 2009
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