added a way to configure the form templates (based on patch #143)

doc/providers/twig.rst

@@ -19,6 +19,9 @@ Parameters
 * **twig.class_path** (optional): Path to where the Twig
   library is located.
 
+* **twig.form.templates** (optional): An array of templates used to render
+  forms (only available when the ``FormServiceProvider`` is enabled).
+
 Services
 --------
 

src/Silex/Provider/TwigServiceProvider.php

@@ -51,9 +51,13 @@ class TwigServiceProvider implements ServiceProviderInterface
                 }
 
                 if (isset($app['form.factory'])) {
-                    $twig->addExtension(new TwigFormExtension(array('form_div_layout.html.twig')));
+                    if (!isset($app['twig.form.templates'])) {
+                        $app['twig.form.templates'] = array('form_div_layout.html.twig');
+                    }
 
-                    // add loader for form_div_layout.html.twig
+                    $twig->addExtension(new TwigFormExtension($app['twig.form.templates']));
+
+                    // add loader for Symfony built-in form templates
                     $reflected = new \ReflectionClass('Symfony\Bridge\Twig\Extension\FormExtension');
                     $path = dirname($reflected->getFileName()).'/../Resources/views/Form';
                     $app['twig.loader']->addLoader(new \Twig_Loader_Filesystem($path));