If a monster leaves the level via a trap that hasn't been discovered by

the player (as can happen if they monster is native to the branch the trap is in), mark it as discovered by the player.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6010 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on June 20, 2008
DKOAL6BFXFEP7XBXZTFN2QKYBPFOBG62OCJFFKOUEW3W3N76PF3AC
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