Lava and deep water now prevent (non-clobber) vaults from being placed. Additionally, items will modify the dungeon square they're placed on so that they are placed on floor or shallow water.
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@5544 c06c8d41-db1a-0410-9941-cceddc491573
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