[ClassLoader] Fix undefined index in ClassCollectionLoader
Merge branch '2.3' into 2.5

* 2.3:
  fix phpdoc's alignment
  Minor phpcs fixes
  [ClassLoader] Fix undefined index in ClassCollectionLoader

Conflicts:
	src/Symfony/Component/Serializer/Encoder/XmlEncoder.php
Merge branch '2.5' into 2.6

* 2.5:
  Added information when an error occured during validation of an answer of a question
  [Console] fixes some typos and phpdoc.
  fix phpdoc's alignment
  Minor phpcs fixes
  [ClassLoader] Fix undefined index in ClassCollectionLoader