docs: update EntityManager#transactional to EntityManager#wrapInTransaction

docs/en/reference/transactions-and-concurrency.rst

@@ -88,29 +88,31 @@ requirement.
 
 A more convenient alternative for explicit transaction demarcation is the use
 of provided control abstractions in the form of
-``Connection#transactional($func)`` and ``EntityManager#transactional($func)``.
+``Connection#transactional($func)`` and ``EntityManager#wrapInTransaction($func)``.
 When used, these control abstractions ensure that you never forget to rollback
 the transaction, in addition to the obvious code reduction. An example that is
 functionally equivalent to the previously shown code looks as follows:
 
 .. code-block:: php
 
     <?php
+    // transactional with Connection instance
+    // $conn instanceof Connection
+    $conn->transactional(function($conn) {
+        // ... do some work
+        $user = new User;
+        $user->setName('George');
+    });
+
+    // transactional with EntityManager instance
     // $em instanceof EntityManager
-    $em->transactional(function($em) {
+    $em->wrapInTransaction(function($em) {
         // ... do some work
         $user = new User;
         $user->setName('George');
         $em->persist($user);
     });
 
-.. warning::
-
-    For historical reasons, ``EntityManager#transactional($func)`` will return
-    ``true`` whenever the return value of ``$func`` is loosely false.
-    Some examples of this include ``array()``, ``"0"``, ``""``, ``0``, and
-    ``null``.
-
 The difference between ``Connection#transactional($func)`` and
 ``EntityManager#transactional($func)`` is that the latter
 abstraction flushes the ``EntityManager`` prior to transaction