Merge branch '4.4' into 5.0

* 4.4:
  [Validator] fix access to uninitialized property when getting value
  [HttpClient] Fix regex bearer
  [Translator] Default value for 'sort' option in translation:update should be 'asc'
  [HttpKernel] Fix stale-if-error behavior, add tests
  [Intl] Provide more locale translations
  [Mailer] Fix STARTTLS support for Postmark and Mandrill
  [Messenger] Check for all serialization exceptions during message dec…
  [Messenger] Fix bug when using single route with XML config
  Fix exception message in Doctrine Messenger
  [DI]  CheckTypeDeclarationsPass now checks if value is type of parameter type
  [SecurityBundle] fix security.authentication.provider.ldap_bind arguments
  Improved error message when no supported user provider is found
  Mysqli doesn't support the named parameters used by PdoAdapter
  Added debug argument to decide if debug page should be shown or not
  Mysqli doesn't support the named parameters used by PdoStore
  Properly handle phpunit arguments for configuration file
  [Mailer] add tests for http transports

User/ChainUserProvider.php

@@ -91,7 +91,7 @@ public function refreshUser(UserInterface $user)
             $e->setUsername($user->getUsername());
             throw $e;
         } else {
-            throw new UnsupportedUserException(sprintf('The account "%s" is not supported.', \get_class($user)));
+            throw new UnsupportedUserException(sprintf('There is no user provider for user "%s". Shouldn\'t the "supportsClass()" method of your user provider return true for this classname?', \get_class($user)));
         }
     }