magic commit that fixe the crash when activating collision after changing cell.

To be faire, this commit should break the collision system... there must be something I don't understand with bullet ghost objects :p

bullet/physic.cpp

@@ -157,7 +157,7 @@ namespace Physic
 
         //TODO: memory leak?
         btOverlappingPairCache* pairCache = new btSortedOverlappingPairCache();
-        pairCache->setInternalGhostPairCallback( new btGhostPairCallback() );
+        //pairCache->setInternalGhostPairCallback( new btGhostPairCallback() );
 
         broadphase = new btDbvtBroadphase(pairCache);