numbers of "doors" involved.
Note (because I forgot to mention it last time): This does look a bit odd in tiles, but it's a cool effect nonethelesss.
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3454 c06c8d41-db1a-0410-9941-cceddc491573
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