When using `--baseurl` before this patch, if a request was made to the
base URL without a trailing / then rclone would return a 404 error.
Unfortunately GVFS / Nautilus makes the request without the /
regardless of what the user put in.
This patch redirects the request to the base URL with a /. So if the
user was using `--baseurl rclone` then a request to
http://localhost/rclone would be redirected with a 308 response to
http://localhost/rclone/Fixes#4814