Background page callbacks without clean url fail.

Hi, I see in your code that you have hard coded the HTTP request path to be "/background-process/start". This doesn't work when clean URLs are off, nor does it work if the site is not in the root of the web server. Changing BackgroundProcess.class.php line 135 to this solves this issue for me:

    $path = url('background-process/start') .'/' . urlencode($this->handle) . '/' . urlencode($this->token);

Note also, that using urlencode like this only works based on certain assumptions of what it is you are encoding. You may be better to look at rawurlencode, potential twice if clean urls are in effect since url encoding is decoded once from clean url rewrite and again by php.