[Yaml] fixed embedded folded string parsing
Merge branch '2.2' into 2.3

* 2.2:
  [Locale] Fixed: StubLocale::setDefault() throws no exception when "en" is passed
  [Yaml] fixed embedded folded string parsing
  [Validator] fixed Boolean handling in XML constraint mappings (closes #5603)

Conflicts:
	src/Symfony/Component/Locale/Stub/StubLocale.php
	src/Symfony/Component/Locale/Tests/Stub/StubLocaleTest.php