Fix 1902749: starving to death by invoking abilities

         (FR, but I consider it a bug)

Players will now be prompted whether they want to use an ability if there's a chance its food_cost might make them starve to death.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3474 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on February 28, 2008
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