Implemented 1591922: monsters coming into view while traveling

trigger a message explaining why travel stopped (on MSGCH_WARN.) Only the base description of the monster is printed, no equipment or such.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@533 c06c8d41-db1a-0410-9941-cceddc491573

Created by  haranp  on November 30, 2006
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