removed unneeded start() calls for the session

doc/providers/security.rst

@@ -173,11 +173,9 @@ Always keep in mind the following two golden rules:
 
 * The ``check_path`` path must always be defined **inside** the secured area.
 
-For the login form to work, create a controller where you start the session::
+For the login form to work, create a controller like the following::
 
     $app->get('/login', function(Request $request) use ($app) {
-        $app['session']->start();
-
         return $app['twig']->render('login.html', array(
             'error'         => $app['security.last_error']($request),
             'last_username' => $app['session']->get('_security.last_username'),

doc/providers/session.rst

@@ -66,7 +66,6 @@ authenticates a user and creates a session for him::
         $password = $app['request']->server->get('PHP_AUTH_PW');
 
         if ('igor' === $username && 'password' === $password) {
-            $app['session']->start();
             $app['session']->set('user', array('username' => $username));
             return $app->redirect('/account');
         }
@@ -78,7 +77,6 @@ authenticates a user and creates a session for him::
     });
 
     $app->get('/account', function () use ($app) {
-        $app['session']->start();
         if (null === $user = $app['session']->get('user')) {
             return $app->redirect('/login');
         }