Fixing Warn(..) function so that it doesn't output into resulting code

src/bind.inc.php

@@ -158,7 +158,11 @@ function add_twig_support(\Twig\Environment $twig)
   $twig->addFunction(new \Twig\TwigFunction('Warn', 
     function($e) 
     {
-      echo "WARN: $e\n";
+      //NOTE: we can't just echo the value because it will
+      //      be rendered into resulting code
+      register_shutdown_function(function() use($e) {
+        echo "WARN: $e\n";
+      });
     }
   ));
   $twig->addFunction(new \Twig\TwigFunction('has_token',