[Components][Serializer] optional constructor arguments can be omitted during the denormalization process
Merge branch '2.3' into 2.4

* 2.3:
  Fixed failed config schema loads due to libxml_disable_entity_loader usage.
  enabled PHP 5.6 for tests
  [Process] Fix ExecutableFinder with open basedir
  Refactored the CssSelector to remove the circular object graph
  Fix mocks to support >=5.5.14 and >=5.4.30
  [ClassLoader] fixed PHP warning on PHP 5.3
  [Components][Serializer] optional constructor arguments can be omitted during the denormalization process
  [DomCrawler] properly handle buttons with single and double quotes inside the name attribute

Conflicts:
	src/Symfony/Component/Serializer/Tests/Normalizer/GetSetMethodNormalizerTest.php