Fix [2488346]: If a monster steps on an ammo-shooting trap, only

poison/hurt it if the ammo actually hit it, and don't display messages like "An [ammo type] misses the [monster], but does no damage!".

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@8283 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on January 6, 2009
RJQE6CVFZ73IORNKEER5HMKQOGNP7W2JVZ5MW6X6NYWA6J7YGAQQC
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