Don't mangle protocol relative URLs in HTML content; fixes #531

Author: following5

okapi/core/Okapi.php

@@ -1127,7 +1127,7 @@ public static function fix_oc_html($html, $text_html)
          */
 
         $html = preg_replace(
-            "~\b(src|href)=([\"'])(?![a-z0-9_-]+:)~",
+            "~\b(src|href)=([\"'])(?![a-z0-9_-]+:|//)~",
             "$1=$2".Settings::get("SITE_URL"),
             $html
         );