Apply patch 1901117: vitrification effect for Xom (and Xom cleanup)

This needs flavour messages, and looks odd for large power because the undiggable stone of the level also gets turned into glass possibly resulting in huge areas of glass tiles.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3464 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on February 25, 2008
22YVHM74WBJNJE4PA5CBEUTDWM6FAGGGILI26A4LXAURX55TNRKAC
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