Prevent trapdoor spider from repeatedly unhiding/hiding in the same turn when

it's heavily damaged and attempting to stay hidden.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8644 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on January 21, 2009
7GA2VVQJWMYVRXJK4A4L3QLI54LOVRUDCTAFOR2IJZ63YEJWG3SAC
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