Moved RatsNest vault to D:4-8 (Erik). We still need some sort of dummy vault to

balance this out since it is the only vault in its depth range, and will be picked all the time if the roll for a vault comes up (1 in 9).

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@996 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dshaligram  on March 8, 2007
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