player_in_a_dangerous_place() can now optionally return if any hostile

invisible monsters are nearby; for future use.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@5967 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on June 18, 2008
UH2EJWY63UWBAHSNW7QVVANX4YPJCBACR3IHCQQP6CTVNOSGSMMAC
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