Move experience draining for players and monsters to the actor

interface, and use it in necromancy miscasts that drain experience.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8496 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on January 17, 2009
LRNA65FNZCSZBRU64O3UBUQ72J6ZL6WCWANADSL5VUAURQXJL6GQC
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