Fix bugs found in first full-scale testing with S3.

- Fix bugs preventing make_day_list_html() from working on S3.
- Fix bug in webfs_s3.rmtree().
- Work around problem with DreamHost's version of boto library in
webfs_s3.move_to_web().
Change to keep html files in incoming dir tree.

- DreamObjects won't resolve to index.html when the URL is a directory
so changed code to leave html files in incoming dir tree for hosting
machine to serve as it used to before S3.
- Update all relevant URLs to point explicitly to index.html rather
than to the directory name.
- Passes unit tests, not tried in real world, yet.