Merge branch 'ma/leakplugs'

Memory leaks in various codepaths have been plugged.

* ma/leakplugs:
  pack-bitmap[-write]: use `object_array_clear()`, don't leak
  object_array: add and use `object_array_pop()`
  object_array: use `object_array_clear()`, not `free()`
  leak_pending: use `object_array_clear()`, not `free()`
  commit: fix memory leak in `reduce_heads()`
  builtin/commit: fix memory leak in `prepare_index()`

commit.c

@@ -1086,6 +1086,7 @@ struct commit_list *reduce_heads(struct commit_list *heads)
 	num_head = remove_redundant(array, num_head);
 	for (i = 0; i < num_head; i++)
 		tail = &commit_list_insert(array[i], tail)->next;
+	free(array);
 	return result;
 }