Fix wall collision coalescing code

app/lib/world/world_utils.coffee

@@ -72,8 +72,12 @@ module.exports.downTheChain = downTheChain = (obj, keyChain, newValue=undefined)
 module.exports.now = (if window?.performance?.now? then (-> window.performance.now()) else (-> new Date()))
 
 module.exports.consolidateThangs = consolidateThangs = (thangs) ->
+  # We can gain a performance increase by consolidating all regular walls into a minimal covering, non-intersecting set a la Gridmancer.
   debug = false
-  isStructural = (t) -> t.stateless and t.collides and t.collisionCategory is 'obstacles' and t.shape in ['box', 'sheet'] and t.restitution is 1.5 and (t.pos.x - t.width / 2 >= 0) and (t.pos.y - t.height / 2 >= 0)
+  isStructural = (t) ->
+    t.stateless and t.collides and t.collisionCategory is 'obstacles' and t.shape in ['box', 'sheet'] and  # Can only do wall-like obstacle Thangs.
+    t.spriteName isnt 'Ice Wall' and t.restitution is 1.0 and  # Fixed restitution value on 2016-03-15, but it causes discrepancies, so disabled for Kelvintaph levels.
+    (t.pos.x - t.width / 2 >= 0) and (t.pos.y - t.height / 2 >= 0)  # Grid doesn't handle negative numbers, so don't coalesce walls below/left of 0, 0.
   structural = _.remove thangs, isStructural
   return unless structural.length
   rightmost = _.max structural, (t) -> t.pos.x + t.width / 2
@@ -101,7 +105,9 @@ module.exports.consolidateThangs = consolidateThangs = (thangs) ->
     thang.pos.y = rect.y
     thang.width = rect.width
     thang.height = rect.height
+    thang.destroyBody()
     thang.createBodyDef()
+    thang.createBody()
     dissection.push thang
 
   dissectRectangles grid, addStructuralThang, false, debug