Explore more efficiently by inferring likely wall tiles when autoexploring
If autoexplore is stopped on the way to an exit (such as by a trap), then it will still go that target when AE is initiated again
When autoexploring don't go to items that the player dropped


git-svn-id: http://svn.net-core.org/repos/t-engine4@4720 51575b47-30f0-44d4-a5cc-537603b46e54