objects around so much. It was getting out of hand.

	* libnautilus-extensions/nautilus-directory-async.c:
	(empty_close_callback): Give a warning if we ever have a close
	that fails.
	(directory_count_callback): For easier debugging, NULL out the
	file after unref'ing.
	(start_getting_directory_counts): Unref the file when we cancel
	a directory count part-way through (leak #1).
	(start_getting_top_lefts): Close the file when we cancel a top
	left read part-way through (leak #2). Unref the file when we
	cancel a top left read part way thorugh (leak #3).