ActionController: Force HTTP redirects in method redirectHttp()

That's what its name implies, right? The counterpart is redirectXhr(),
which does still its job. redirectNow() on the other hand is for the
lazy people.

library/Icinga/Web/Controller/ActionController.php

@@ -424,6 +424,10 @@ class ActionController extends Zend_Controller_Action
 
     protected function redirectHttp($url)
     {
+        if ($this->isXhr()) {
+            $this->getResponse()->setHeader('X-Icinga-Redirect-Http', 'yes');
+        }
+
         $this->getResponse()->redirectAndExit($url);
     }