Fix broken minivault placement guarantee: minivaults could be placed without overlapping existing floor squares.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@10498 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dshaligram  on August 7, 2009
5Q3VAMQ3MWU46LY42OB6GAILLDJE6NGKR2L4SJWLLCXLPRSPLVFQC
Change contents