updated base64.js to version 2.1.9, using minified version found at

9192c510f5/base64.min.js
kudos Dan Kogai

small improvements to input checking
implementing default values for most configuration options
switching to versioned JS files to avoid version hack used in template

lib/persistence.php

@@ -87,7 +87,8 @@ abstract class persistence
             file_put_contents(
                 $file,
                 'Allow from none' . PHP_EOL .
-                'Deny from all'. PHP_EOL
+                'Deny from all'. PHP_EOL,
+                LOCK_EX
             );
         }
     }