[CR] Danger update: stairs, pushing, surrounding by stumbling

updated again :)

* allows mobs to arrive on 1 of the 4 closest stairs
   * " they pick the alternate rail from time to time as they bumble down sthe stairs..
   * it used to pick the closest one it found first. i have it make another pass to pull out more stairs at that distance or +1.

* fixes some logic in the mob->player pushing code
   - had a semantic error that had it pushing too rarely,  
   - was pushing, making invisible.. so its now looking to mon_at() before can_move_to().

* adds monster -> monster pushing to game stair-handling
   - coming up/down, mobs can also stumble into other mobs still on the stairs.

* adds monster -> monster pushing to monmove ai
   - (low chance) mobs stumble into other mobs

* pushed mobs have a 25% chance of being "downed".

* fuzzyfies targeting when very close
   - monsters sometimes flail to the players side.
   - monsters sometimes rebase themselves instead of aiming for the shortest path
   - monsters infrequently take an altogether random step. (not a stumble)
   - the slightly lower monster dps
      - ends all the typical kiting exploits. as mobs can now enter the room while you're standing there before the window... they do that really really slowly thow. .. they step of fires/bushes and wind up on your side as they stumble 
       - enables mobs to slide past obstacles from time to time. 

* i kept the lovely 'combine-location-guessing-with-randomize-activation' implementation style.

please get some gear and playtest a surrounded start 
it kinda makes encounters more memorable in some small way.