changed debug to have a sensible default in all providers

src/Silex/Provider/HttpCacheServiceProvider.php

@@ -31,7 +31,7 @@ class HttpCacheServiceProvider implements ServiceProviderInterface, EventListene
         $app['http_cache'] = $app->share(function ($app) {
             $app['http_cache.options'] = array_replace(
                 array(
-                    'debug' => $app['debug'],
+                    'debug' => isset($app['debug']) ? $app['debug'] : false,
                 ), $app['http_cache.options']
             );
 

src/Silex/Provider/HttpFragmentServiceProvider.php

@@ -31,7 +31,7 @@ class HttpFragmentServiceProvider implements ServiceProviderInterface, EventList
     public function register(\Pimple $app)
     {
         $app['fragment.handler'] = $app->share(function ($app) {
-            return new FragmentHandler($app['fragment.renderers'], $app['debug'], $app['request_stack']);
+            return new FragmentHandler($app['fragment.renderers'], isset($app['debug']) ? $app['debug'] : false, $app['request_stack']);
         });
 
         $app['fragment.renderer.inline'] = $app->share(function ($app) {

src/Silex/Provider/MonologServiceProvider.php

@@ -50,7 +50,7 @@ class MonologServiceProvider implements ServiceProviderInterface, BootableProvid
 
             $log->pushHandler($app['monolog.handler']);
 
-            if ($app['debug'] && isset($app['monolog.handler.debug'])) {
+            if (isset($app['debug']) && $app['debug'] && isset($app['monolog.handler.debug'])) {
                 $log->pushHandler($app['monolog.handler.debug']);
             }
 

src/Silex/Provider/TwigServiceProvider.php

@@ -38,15 +38,15 @@ class TwigServiceProvider implements ServiceProviderInterface
             $app['twig.options'] = array_replace(
                 array(
                     'charset'          => $app['charset'],
-                    'debug'            => $app['debug'],
-                    'strict_variables' => $app['debug'],
+                    'debug'            => isset($app['debug']) ? $app['debug'] : false,
+                    'strict_variables' => isset($app['debug']) ? $app['debug'] : false,
                 ), $app['twig.options']
             );
 
             $twig = new \Twig_Environment($app['twig.loader'], $app['twig.options']);
             $twig->addGlobal('app', $app);
 
-            if ($app['debug']) {
+            if (isset($app['debug']) && $app['debug']) {
                 $twig->addExtension(new \Twig_Extension_Debug());
             }