Simplify mutation handling again, and add a message for when Zin's

mutation protection takes effect.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@4686 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on April 26, 2008
UCM6RM43UZHOSRI75MQQZPBTLQIV63N4KQ4V7N54ZZGQ7LCR6YGQC
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