FIX: Use new resource loading syntax for javascript

SilverStripe 4 vendormodule types make use of an 'expose' composer
directive to allow assets they provide to be accessed by a web request.
Previously the javascript for the iFrame resizing business tried to load
from a static path that no longer exists (referenced inside PHP), which
caused a fatal error. This has been fixed along with making the
conditional code for enforcing a protocol on the page's request a bit more
readable & easily digestable to developers.

code/IFramePageController.php

@@ -11,17 +11,19 @@ class IFramePageController extends ContentController
     protected function init()
     {
         parent::init();
-
-        if ($this->ForceProtocol) {
-            if ($this->ForceProtocol == 'http://' && Director::protocol() != 'http://') {
-                return $this->redirect(preg_replace('#https://#', 'http://', $this->AbsoluteLink()));
-            } elseif ($this->ForceProtocol == 'https://' && Director::protocol() != 'https://') {
-                return $this->redirect(preg_replace('#http://#', 'https://', $this->AbsoluteLink()));
-            }
+        $currentProtocol = Director::protocol();
+        $desiredProtocol = $this->ForceProtocol;
+        if ($desiredProtocol && $currentProtocol !== $desiredProtocol) {
+            $enforcedLocation = preg_replace(
+                "#^${currentProtocol}#",
+                $desiredProtocol,
+                $this->AbsoluteLink()
+            );
+            return $this->redirect($enforcedLocation);
         }
 
         if ($this->IFrameURL) {
-            Requirements::javascript('iframe/javascript/iframe_page.js');
+            Requirements::javascript('silverstripe/iframe: javascript/iframe_page.js');
         }
     }
 }