Allow HTTP redirection to use relative location

 * When redirecting a request with HTTP code 302, the given URL may be
relative. This is currently nonstandard, but so widely used that the
drafts for HTTP 1.1 update include it.
 * When the URL starts with a dot character, we simply append it to the
original request location, and let the server resolve the relative path
itself.
 * Automatic whitespace cleanup.