Merge branch '4.2' into 4.3

* 4.2:
  When overriding `session` service definition, make it public

Author: javiereguiluz

session.rst

@@ -180,6 +180,7 @@ the default ``AttributeBag`` by the ``NamespacedAttributeBag``:
 
         # config/services.yaml
         session:
+            public: true
             class: Symfony\Component\HttpFoundation\Session\Session
             arguments: ['@session.storage', '@session.namespacedattributebag', '@session.flash_bag']