Add res_rotting() method to the actor class so that the "are you the right

type of undead to resist rotting" logic can be in just one place instead of duplicated every time the check is made.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6354 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on July 2, 2008
6LTQT4CP7LJZLAE7JTPQ4OT4JOG3IFYM7RNXL3FINKBFO6452DTAC
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