By not redirecting when we are already on the purge caches page we
can preserve the submitted form data, allowing users to easily
repeat the previous action.
If you click the link in the page footer, then it will reliably
redirect you back to the page you were on after purging the caches.
If you go to the purge all caches page in the admin menu, it shows you a
purge button, with no cancel button. Clicking the button purges the
caches and takes you back to the page with the button.
