Merge branch '4.4' into 5.2

* 4.4:
  Add part about resolving parameter values to prepend extension
  Unique validator: Better description for the value placeholder

Author: javiereguiluz

bundles/prepend_extension.rst

@@ -82,6 +82,11 @@ in case a specific other bundle is not registered::
 
         // process the configuration of AcmeHelloExtension
         $configs = $container->getExtensionConfig($this->getAlias());
+
+        // resolve config parameters e.g. %kernel.debug% to its boolean value
+        $resolvingBag = $container->getParameterBag();
+        $configs = $resolvingBag->resolveValue($configs);
+        
         // use the Configuration class to generate a config array with
         // the settings "acme_hello"
         $config = $this->processConfiguration(new Configuration(), $configs);

reference/constraints/Unique.rst

@@ -120,7 +120,7 @@ You can use the following parameters in this message:
 =============================  ================================================
 Parameter                      Description
 =============================  ================================================
-``{{ value }}``                The repeated value
+``{{ value }}``                The current (invalid) value
 =============================  ================================================
 
 .. include:: /reference/constraints/_payload-option.rst.inc