Initial work on generating markers.js from signposts

Details:
 * A queue object is passed to all renderers, allowing each process to
   avoid using shared memory when recording signpost data.
 * New overviewer.dat file that stores persistent data between runs.
   Currently used to store information on signs.  markers.js is
   generated by merging the stored POI list with the newly generated POI
   list.
 * POIs are tagged with their type (e.g. "spawn" or "sign").  This
   should be useful if different types of POIs needs to be
   handled/displayed differently

Known bugs:
 * If you delete the last sign in a chunk, it won't be removed from
   markers.js

quadtree.py

@@ -25,6 +25,7 @@ import collections
 import json
 import logging
 import util
+import cPickle
 
 from PIL import Image
 
@@ -143,12 +144,33 @@ class QuadtreeGen(object):
         if not os.path.exists(tileDir): os.mkdir(tileDir)
         blank.save(os.path.join(tileDir, "blank."+self.imgformat))
 
+
         if skipjs:
             return
 
+        # since we will only discover PointsOfInterest in chunks that need to be 
+        # [re]rendered, POIs like signs in unchanged chunks will not be listed
+        # in self.world.POI.  To make sure we don't remove these from markers.js
+        # we need to merge self.world.POI with the persistant data in world.PersistentData
+
+        # 
+        modifiedChunks = map(lambda x: x['chunk'], filter(lambda x: x['type'] != 'spawn', self.world.POI))
+       
+        for item in self.world.persistentData['POI']:
+            # if this previously discovered POI isn't in a modified chunk, keep it
+            if item['chunk'] not in modifiedChunks and item['type'] != 'spawn':
+                self.world.POI.append(item)
+            # else discard it, because self.world.POI will contain it (or not if it
+            # was deleted)
+
         # write out the default marker table
         with open(os.path.join(self.destdir, "markers.js"), 'w') as output:
             output.write("var markerData=%s" % json.dumps(self.world.POI))
+        
+        # save persistent data
+        self.world.persistentData['POI'] = self.world.POI
+        with open(self.world.pickleFile,"wb") as f:
+            cPickle.dump(self.world.persistentData,f)
 
         # write out the default (empty, but documented) region table
         with open(os.path.join(self.destdir, "regions.js"), 'w') as output: