Natural sorting fix: assure that directories are sorted always before files as Ellen has recommended. One minor issue is left: when the sort order is descending, the natural sorting result is:
 item 10.jpg
 item 11.jpg
 item 2.jpg
 item 1.jpg
instead of
 item 11.jpg
 item 10.jpg
 item 2.jpg
 item 1.jpg

svn path=/trunk/playground/utils/dolphin/; revision=622751