Tell AI to avoid edges, especially ones over water (this does not include checking whether a knock could drown yet). Also make flakes pick a new random dx/dy on respawn to further reduce patterns. Also disable a couple of weapons for the particularly dumb AI levels, and disable switching for the dumbest.
306cedbeb213
fixed several 'retina display' images and added a bunch more (though just from upscaling the normal ones; might be nice to have 'em redrawn at a real higher resolution)
