Merge branch 'ew/free-island-marks'

"git pack-objects" learned to release delta-island bitmap data when
it is done using it, saving peak heap memory usage.

* ew/free-island-marks:
  delta-islands: free island_marks and bitmaps

builtin/pack-objects.c

@@ -929,8 +929,10 @@ static struct object_entry **compute_write_order(void)
 	 */
 	for_each_tag_ref(mark_tagged, NULL);
 
-	if (use_delta_islands)
+	if (use_delta_islands) {
 		max_layers = compute_pack_layers(&to_pack);
+		free_island_marks();
+	}
 
 	ALLOC_ARRAY(wo, to_pack.nr_objects);
 	wo_end = 0;