Merge branch '2.8' into 3.2

* 2.8:
  property constraints can be added in child classes
  added test for staticClassLoader in LazyLoadingMetadatafactory
  spelling fixes
  Readd Symfony version status in the toolbar
  make sure that null can be the invalid value
  [VarDumper] Improve dump of AMQP* Object
  [VarDumper] Fixed dumping of terminated generator
  bumped Symfony version to 2.8.18
  updated VERSION for 2.8.17
  updated CHANGELOG for 2.8.17
  bumped Symfony version to 2.7.25
  updated VERSION for 2.7.24
  update CONTRIBUTORS for 2.7.24
  updated CHANGELOG for 2.7.24
  [FrameworkBundle] Simplify createPackageDefinition
  fix directory resource considers same timestamp not fresh
  return false early from directory resource

Loader/MoFileLoader.php

@@ -137,7 +137,7 @@ protected function loadResource($resource)
     }
 
     /**
-     * Reads an unsigned long from stream respecting endianess.
+     * Reads an unsigned long from stream respecting endianness.
      *
      * @param resource $stream
      * @param bool     $isBigEndian