[1944570] Fixing bug where the unexplored stairs marker wasn't being saved for tiles (due to only storing shorts, which truncated off that flag.) Unsurprisingly, this breaks saves with tiles.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@4373 c06c8d41-db1a-0410-9941-cceddc491573

Created by  ennewalker  on April 19, 2008
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