Fix memory leaks caused by reused arrays of Spatials

jme3-core/src/main/java/com/jme3/scene/Spatial.java

@@ -706,15 +706,21 @@ void checkDoTransformUpdate() {
                 i++;
             }
 
-            vars.release();
-
             for (int j = i; j >= 0; j--) {
                 rootNode = stack[j];
+                // Clear stack to avoid memory leaks
+                // (Spatials added to the stack might get detached from their parent
+                // after this method has been called -> they and their OGL object will not 
+                // get garbage collected when subsequent calls to checkDoTransformUpdate() 
+                // require only smaller stacks)
+                stack[j] = null;
                 //rootNode.worldTransform.set(rootNode.localTransform);
                 //rootNode.worldTransform.combineWithParent(rootNode.parent.worldTransform);
                 //rootNode.refreshFlags &= ~RF_TRANSFORM;
                 rootNode.updateWorldTransforms();
             }
+
+            vars.release();
         }
     }
 

jme3-core/src/main/java/com/jme3/util/ListSort.java

@@ -31,6 +31,7 @@
  */
 package com.jme3.util;
 
+import java.util.Arrays;
 import java.util.Comparator;
 
 /**
@@ -240,8 +241,14 @@ public void sort(T[] array, Comparator<T> comparator) {
         }
 
         // Merge all remaining runs to complete sort        
-        mergeForceCollapse();        
-
+        mergeForceCollapse();     
+
+        // Clear temporary array to avoid memory leaks
+        // (e.g. Geometries added to the array by GeometryList#sort() might get
+        // detached from their parent later -> they and their OGL object will not
+        // get garbage collected when subsequent sorts use only portions of the
+        // array)
+        Arrays.fill(tmpArray, null);
     }
 
     /**