New ajax command to do proper redirect for ajax processes

This is a new command which will allow doing a redirect in an ajax call. This will do it so that it will do another post to the redirected URL so that Drupal will treat the new call as an AJAX call so that things like ajax_page_state will get past so that libraries will not get loaded again.

I am not sure if the JS is exactly right but I could not work out the best way to run the ajax outside the previous success call, so I think that will be more elegant.

I required this to handle a AJAX wizard in ctools. see #2917879 for more information.