Replace Yred's life saving with injury mirroring, based on the old "pain

mirror" FR with some suggestions from dploog. A monster affected by this will briefly flash blood-red, and each mirroring costs the square root of the damage in piety. It will not damage a monster if the damage kills you first, but that should only have an effect on gameplay in wizard mode if you use it to avoid death, in which case you don't really need it.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6983 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on September 25, 2008
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