Twig compiler tweak: shows name of rendered template

Twig\Node\Module.php

    protected function compileDisplayBody(Twig_Compiler $compiler)
    {
        $filename = $this->getAttribute('filename');
        $compiler->write("echo '<!-- START " . $filename . (null !== $this->getNode('parent') ? " (has parent)" : '') . " -->';\n");
        $compiler->subcompile($this->getNode('body'));

        if (null !== $this->getNode('parent')) {
            if ($this->getNode('parent') instanceof Twig_Node_Expression_Constant) {
                $compiler->write("\$this->parent");
            } else {
                $compiler->write("\$this->getParent(\$context)");
            }
            $compiler->raw("->display(\$context, array_merge(\$this->blocks, \$blocks));\n");
        }
        $compiler->write("echo '<!-- END " . $filename . " -->';\n");
    }