Increase efficiency for pathfinding around glass structures by lowering

the chance to "try again" if the last time we were unsuccessful. Also, if a monster tries to find a path to the player (not directly reachable) and fails, mark all surrounding monsters of the same species within a radius of 2 as having been unsuccessful. This includes monsters that are currently out of los of the player or that are targetting a different monster. Once they target the player, there'll either be a direct path which they can use, or there won't, in which case there's a low chance of using path finding; otherwise they'll simply advance the traditional way as close as they can get.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@5733 c06c8d41-db1a-0410-9941-cceddc491573

Created by  j-p-e-g  on June 11, 2008
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