Fixed some memory leaks.

app/lib/surface/SpriteBoss.coffee

@@ -161,6 +161,7 @@ module.exports = class SpriteBoss extends CocoClass
     thang = sprite.thang
     delete @sprites[sprite.thang.id]
     @spriteArray.splice @spriteArray.indexOf(sprite), 1
+    @stopListening sprite
     sprite.destroy()
     sprite.thang = thang  # Keep around so that we know which thang the destroyed thang was for
 

app/models/ThangType.coffee

@@ -62,7 +62,9 @@ module.exports = class ThangType extends CocoModel
     @options = @fillOptions options
     key = @spriteSheetKey(@options)
     if ss = @spriteSheets[key] then return ss
-    return key if @building[key]
+    if @building[key]
+      @options = null
+      return key
     @t0 = new Date().getTime()
     @initBuild(options)
     @addGeneralFrames() unless @options.portraitOnly
@@ -159,6 +161,7 @@ module.exports = class ThangType extends CocoModel
     @spriteSheets[key] = spriteSheet
     delete @building[key]
     @builder = null
+    @options = null
     spriteSheet
 
   onBuildSpriteSheetComplete: (e, data) ->